Process for producing hydrogenated alpha-olefin- dicyclopentadiene copolymer, method for molding the same and optical material

ABSTRACT

Process for producing a hydrogenated α-olefin-dicyclopentadiene copolymer. The process includes a step of distilling of unreacted dicyclopentadiene or tetrahydrodicyclopentadiene which is a hydrogenated product of unreacted dicyclopentadiene from a mixture containing α-olefin-dicyclopentadiene copolymer or its hydrogenated product in the presence of a high-boiling hydrocarbon solvent having a boiling point of 195 to 300° C. and an ignition point of 260° C. or more. Method for melt molding the hydrogenated α-olefin-dicyclopentadiene copolymer is also proposed.

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a process for producing ahydrogenated α-olefin-dicyclopentadiene copolymer, a method for moldingthe same and an optical material obtained from the same.

[0002] Alpha-olefin-cyclic olefin copolymers obtained by theaddition-copolymerization of an α-olefin and a cyclic olefin aresynthetic resins having excellent transparency, heat resistance,weatherability, chemical resistance, solvent resistance, dielectriccharacteristics and various mechanical properties and are widely used invarious fields.

[0003] These α-olefin-cyclic olefin copolymers are generally produced bythe addition-copolymerization of an α-olefin and a cyclic olefin in ahydrocarbon-based solvent such as toluene, cyclohexane or hexane in thepresence of an addition polymerization catalyst.

[0004] When a copolymer of an α-olefin and a cyclic olefin having atleast two double bonds between carbons, namely, a cyclic polyene, isused as a resin, the double bonds between carbons contained in thecopolymer must be saturated by hydrogenation to improve heat resistance,weatherability and light resistance. The hydrogenation of a polymer isgenerally carried out through a reaction between a copolymer andhydrogen in the presence of a heterogeneous or homogeneous hydrogenationcatalyst.

[0005] The inventors of the present invention have found that, amongα-olefin-cyclic polyene copolymers, an α-olefin-dicyclopentadienecopolymer, which is obtained when dicyclopentadiene is used as a cyclicpolyene, does not contain the linkages of the dicyclopentadiene and hashigh chemical homogeneity and that a hydrogenatedα-olefin-dicyclopentadiene copolymer is particularly excellent inoptical homogeneity and transparency and suitable for use as an opticalmaterial for an optical disk substrate or the like and have previouslyproposed the copolymer (WO98/33830).

[0006] The hydrogenated α-olefin-dicyclopentadiene copolymer isgenerally produced through the step of polymerizing an α-olefin anddicyclopentadiene in a hydrocarbon solvent, the step of hydrogenatingthe obtained α-olefin-dicyclopentadiene copolymer, the step of removingthe catalyst and the step of removing volatile components.

[0007] In the polymerization reaction step, in order to obtain acopolymer having high chemical homogeneity, it is extremely important tomaintain the ratio of the α-olefin to the dicyclopentadiene at a valuehigher than a predetermined value. As a result, unreacteddicyclopentadiene inevitably remains in a solution after polymerization.In the subsequent hydrogenation reaction step, the residualdicyclopentadiene is hydrogenated together with the copolymer to beconverted into tetrahydrodicyclopentadiene and eventually separated fromthe hydrogenated copolymer together with the solvent in the step ofremoving volatile components.

[0008] The ignition point of the by-produced tetrahydrodicyclopentadieneis 235° C., which is much lower than that of a commonly used solvent(toluene: 480° C., cyclohexane: 260° C.). Therefore, it is not preferredfrom the viewpoint of preventing a danger to keep a polymer solutioncontaining tetrahydrodicyclopentadiene at a temperature higher than 235°C. in ordinary equipment, even if it is in an inert atmosphere. Thisproblem can be solved by using perfect airtight equipment but a greatload is imposed on equipment in an industrial-scale production.Therefore, it is very difficult to produce the hydrogenatedα-olefin-dicyclopentadiene copolymer on an industrial scale.

[0009] JP-A 64-54011, JP-A 5-17527 and JP-A 8-239415 (the term “JP-A” asused herein means an “unexamined published Japanese patent application”)disclose solvents used for a copolymerization reaction between anα-olefin and dicyclopentadiene and JP-A 63-243103 discloses a solventused for the hydrogenation reaction of an ethylene-dicyclopentadienecopolymer. Most of the solvents are compounds having a boiling pointlower than the boiling point of tetrahydrodicyclopentadiene (194° C. at760 mmHg). When a solvent having such a low boiling point is used, thesolvent is first distilled off in the step of removing volatilecomponents and then tetrahydrodicyclopentadiene is distilled off.However, when the solvent is almost completely distilled off, thehydrogenated copolymer becomes solid at a temperature lower than theignition point of tetrahydrodicyclopentadiene, thereby making itextremely difficult to completely distill offtetrahydrodicyclopentadiene. Some solvents having a boiling point higherthan that of tetrahydrodicyclopentadiene are also enumerated. All ofthem, however, have a high melting point and are not suitable for use ina polymerization reaction or have a low ignition point of around 250° C.or low solubility for polymers. Therefore, they cannot be used in actualproduction.

[0010] As described above, tetrahydrodicyclopentadiene cannot be removedfrom the copolymer solution safely and efficiently by conventionallyknown methods.

[0011] When a commonly used hydrocarbon-based solvent such as toluene orcyclohexane is used, there arises another serious problem to be solvedin the step of removing volatile components. Since the boiling point ofthe hydrocarbon-based solvent is lower than the melting temperature ofthe polymer by 100° C. or more, the polymer becomes solid when thesolvent is completely distilled off, thereby making stirring extremelydifficult. It is possible to obtain a molten polymer without passingthrough a solid state by carrying out the operation of removing volatilecomponents in a pressurization system and increasing the boiling pointof the solvent. However, the control of a reaction is extremelydifficult and a great load is imposed on equipment. Thus, there has beenno method for directly converting the polymer from a solution state intoa molten state with ease, and the development of this method has beendesired.

[0012] On the other hand, not only transparency but also variouscharacteristic properties such as optical isotropy (low birefringence),dimensional stability, weatherability and thermal stability are requiredfor plastics used as an optical material for optical disk substrates andoptical lenses and the like. For these optical applications,polycarbonates and poly(methyl methacrylate) have been mainly used.However, molded products of polycarbonates are liable to show opticalanisotropy due to large specific birefringence, whereas poly(methylmethacrylate) are inferior in dimensional stability due to extremelyhigh water absorption and have low heat resistance. Althoughpolycarbonates are mainly used for optical disk substrates nowadays,there arise concerns about such problems as the large birefringence ofthe polycarbonates and the warp of a disk by moisture absorption, alongwith a recent attempt to increase the capacity of a magneto-opticalrecording disk (MOD) or to increase the recording density as typified bythe development of a digital video disk (DVD).

[0013] In view of the above situation, the development of cyclic olefinpolymers as substitutes for polycarbonates is now under way intensively.These cyclic olefin-based resins are expected to be used asthermoplastic transparent resins having small birefringence and highheat resistance for an optical material for optical lenses and opticalsheets in addition to optical disk substrates.

[0014] It is an object of the present invention to provide a process forproducing a hydrogenated α-olefin-dicyclopentadiene copolymer.

[0015] It is another object of the present invention to provide aprocess for producing a hydrogenated α-olefin-dicyclopentadienecopolymer, which is capable of removing unreacted dicyclopentadiene ortetrahydrodicyclopentadiene, which is the hydrogenated product ofdicyclopentadiene, safely and efficiently.

[0016] It is still another object of the present invention to provide amethod for melt molding of a hydrogenated α-olefin-dicyclopentadienecopolymer.

[0017] It is a further object of the present invention to provide amethod for melt molding of a hydrogenated α-olefin-dicyclopentadienecopolymer, which is suitable for producing an optical material that israrely colored and free from a fish eye or silver streak and that hasexcellent transparency and moldability, such as an optical disksubstrate, optical lens or optical sheet.

[0018] It is a still further object of the present invention to providean optical material obtained by the melt molding method of the presentinvention.

[0019] Other objects and advantages of the present invention will becomeapparent from the following description.

[0020] According to the present invention, firstly, the above objectsand advantages of the present invention are attained by a process forproducing a hydrogenated α-olefin-dicyclopentadiene copolymer (may bereferred to as “the first production process of the present invention”=0hereinafter) comprising:

[0021] (1) the step of addition-polymerization of an α-olefin having 2or more carbon atoms and dicyclopentadiene in a hydrocarbon solvent inthe presence of a polymerization catalyst, and then removing thepolymerization catalyst as required, to produce anα-olefin-dicyclopentadiene copolymer solution containing unreacteddicyclopentadiene;

[0022] (2) the step of adding a hydrogenation catalyst to the copolymersolution produced in the step (1) to hydrogenate the unsaturated doublebonds of the α-olefin-dicyclopentadiene copolymer so as to produce amixture containing a hydrogenated α-olefin-dicyclopentadiene copolymer;and

[0023] (3) the step of distilling off tetrahydrodicyclopentadiene formedin the hydrogenation reaction of the step (2) from the mixturecontaining a hydrogenated α-olefin-dicyclopentadiene copolymer producedin the previous step,

[0024] wherein at least one of the following operations (i), (ii) and(iii) is carried out to ensure that a high-boiling hydrocarbon solventis existent in an amount of at least 100 parts by weight based on 100parts by weight of the hydrogenated α-olefin-dicyclopentadiene copolymerat the end of the step (3):

[0025] (i) use of a high-boiling hydrocarbon solvent as at least part ofthe hydrocarbon solvent of the step (1),

[0026] (ii) addition of a high-boiling hydrocarbon solvent in the step(2), and

[0027] (iii) addition of a high-boiling hydrocarbon solvent in the step(3); and the high-boiling hydrocarbon solvent contains at least ahydrocarbon solvent having a boiling point at normal pressure of 195 to300° C. and an ignition point of 260° C. or more.

[0028] Secondly, the above objects and advantages of the presentinvention are attained by a process for producing a hydrogenatedα-olefin-dicyclopentadiene copolymer (may be referred to as “the secondproduction process of the present invention” hereinafter) comprising:

[0029] (1′) the step of addition-polymerizing an α-olefin having 2 ormore carbon atoms and dicyclopentadiene in a hydrocarbon solvent in thepresence of a polymerization catalyst, and then removing thepolymerization catalyst as required, to produce anα-olefin-dicyclopentadiene copolymer solution containing unreacteddicyclopentadiene;

[0030] (2′) the step of distilling off the unreacted dicyclopentadienefrom the α-olefin-dicyclopentadiene copolymer solution containing theunreacted dicyclopentadiene produced in the step (1′) to produce anα-olefin-dicyclopentadiene copolymer solution containing substantiallyno dicyclopentadiene; and

[0031] (3′) adding a hydrogenation catalyst to theα-olefin-dicyclopentadiene copolymer solution produced in the previousstep to hydrogenate the unsaturated double bonds of theα-olefin-dicyclopentadiene copolymer to produce a mixture containing ahydrogenated α-olefin-dicyclopentadiene copolymer,

[0032] wherein at least one of the following operations (i′) and (ii′)is carried out to ensure that a high-boiling hydrocarbon solvent isexistent in an amount of at least 100 parts by weight based on 100 partsby weight of the α-olefin-dicyclopentadiene copolymer at the end of theabove step (2′):

[0033] (i′) use of a high-boiling hydrocarbon solvent as at least partof the hydrocarbon solvent of step (1′), and

[0034] (ii′) addition of a high-boiling hydrocarbon solvent in step(2′); and the high-boiling hydrocarbon solvent contains at least ahydrocarbon solvent having a boiling point at normal pressure of 195 to300° C. and an ignition point of 260° C. or more.

[0035] The melt molding method and the optical material of the presentinvention will be described later.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 shows the relationship between the solution viscosity andtemperature T (K) of a hydrogenated α-olefin-dicyclopentadiene copolymerdissolved in toluene obtained in Reference Example 1 when the solutionconcentration is used as a parameter;

[0037]FIG. 2 shows the relationship between the solution viscosity andtemperature of a hydrogenated α-olefin-dicyclopentadiene copolymerdissolved in tetrahydronaphthalene obtained in Reference Example 1 whenthe solution concentration is used as a parameter;

[0038]FIG. 3 shows the relationship (straight line J) between thesolution viscosity at 110° C. of a hydrogenatedα-olefin-dicyclopentadiene copolymer dissolved in toluene obtained inReference Example 1 and the solution concentration and the relationship(straight line K) between the solution viscosity at 208° C. of thehydrogenated α-olefin-dicyclopentadiene copolymer dissolved intetrahydronaphthalene and the solution concentration;

[0039]FIG. 4 shows change of time in the composition of a hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 1 inthe step of removing volatile components from the solution;

[0040]FIG. 5 shows change of time in the composition of a hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in ComparativeExample 1 in the step of removing volatile components from the solution;

[0041]FIG. 6 shows change of time in the composition of a hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 2 inthe step of removing volatile components from the solution; and

[0042]FIG. 7 shows change of time in the composition of a hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 3 inthe step of removing volatile components from the solution.

[0043] First of all, the first production process of the presentinvention will be described in detail hereinafter.

[0044] (step (1))

[0045] The step (1) in the present invention comprisesaddition-copolymerization of an α-olefin having 2 or more carbon atomsand dicyclopentadiene in a hydrocarbon-based solvent in the presence ofa polymerization catalyst, and then removing the polymerization catalystas required, to obtain an α-olefin-dicyclopentadiene copolymercontaining unreacted dicyclopentadiene.

[0046] Illustrative examples of the α-olefin having 2 or more carbonatoms include α-olefins having 2 to 20 carbon atoms such as ethylene,propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene,1-octene and 1-decene. Of these, ethylene and propylene are preferred,and ethylene is particularly preferred from the viewpoint ofpolymerization activity and the molecular weight of the polymer. Theymay be used alone or in combination of two or more.

[0047] Dicyclopentadiene is used as a cyclic olefin in the presentinvention. In consideration of the physical properties of the polymer, acyclic olefin represented by the following general formulas (I) and/or(II) may further be added to dicyclopentadiene as required, preferablyin an amount of 10 mol % or less, more preferably 5 mol % or less.

[0048] [In the formula (I), n is 0 or 1. m is 0 or a positive integer,preferably 0 or 1. P is 0 or 1. R³ to R²² are the same or different andare each a hydrogen atom, halogen atom, aromatic hydrocarbon grouphaving 6 to 10 carbon atoms, or saturated or unsaturated aliphatichydrocarbon group having 1 to 12 carbon atoms, R¹⁹ and R²⁰, or R²¹ andR²² may form an alkylidene group, and one of R¹⁹ and R²⁰ and one of R²¹or R²² may form a ring, which may have a double bond or an aromaticring.]

[0049] [In the formula (II), q is an integer of 2 to 8.]

[0050] The following compounds are examples of the cyclic olefinrepresented by the above formula (I):

[0051] bicyclo[2.2.1]hept-2-ene derivatives such asbicyclo[2.2.1]hept-2-ene(norbornene), 1-methylbicyclo[2.2.1]hept-2-ene,6-methylbicyclo[2.2.1]hept-2-ene, 6-ethylbicyclo[2.2.1]hept-2-ene,6-n-propylbicyclo[2.2.1]hept-2-ene, 6-isopropylbicyclo[2.2.1]hept-2-ene,6-n-butylbicyclo[2.2.1]hept-2-ene, 6-isobutylbicyclo[2.2.1]hept-2-ene,6-ethylidenebicyclo[2.2.1]hept-2-ene,6-propylidenebicyclo[2.2.1]hept-2-ene,6-isopropylidenebicyclo[2.2.1]hept-2-ene and7-methylbicyclo[2.2.1]hept-2-ene; tricyclo[4.3.0.1^(2.5)]-3-decenederivatives such as tricyclo[4.3.0.1^(2.5)]-3-decene,2-methyltricyclo[4.3.0.1^(2.5)]-3-decene,5-methyltricyclo[4.3.0.1^(2.5)]-3-decene and10-methyltricyclo[4.3.0.1^(2.5)]-3-decene;tricyclo[4.4.0.1^(2.5)]-3-undecene derivatives such astricyclo[4.4.0.1^(2.5)]-3-undecene,2-methyltricyclo[4.4.0.1^(2.5)]-3-undecene,5-methyltricyclo[4.4.0.1^(2.5)]-3-undecene and11-methyltricyclo[4.4.0.1^(2.5)]-3-undecene;tetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene derivatives such astetracyclo[4.4.0. 1^(2.5).1^(7.10)]-3-dodecene,8-methyltetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-methyltetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-n-propyltetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-isopropyltetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-n-butyltetracyclo [4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-isobutyltetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-ethylidenetetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene,8-n-propylidenetetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene and8-isopropylidenetetracyclo[4.4.0.1^(2.5).1^(7.10)]-3-dodecene;pentacyclo[6.5.1.1^(3.6).0^(2.7).0^(9.13)]-4-pentadecene andpentacyclo[6.5.1.1^(3.6).0^(2.7).0^(0.13)]-4,10-pentadecadiene.

[0052] Illustrative examples of the compound represented by the formula(II) are as follows: cyclopropene, cyclobutene, cyclopentene,cyclohexene, cycloheptene and cyclooctene.

[0053] The hydrocarbon solvent used in the present invention is notparticularly limited as long as it dissolves the polymerizationcatalyst, the hydrogenation homogeneous catalyst and the producedcopolymer. Preferred examples of the hydrocarbon-based solvent includealiphatic hydrocarbons such as butane, isobutane, pentane, hexane,2-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, heptane,octane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, nonane,2,2,5-trimethylhexane and decane; alicyclic hydrocarbons such ascyclopentane, methylcyclopentane, ethylcyclopentane, cyclohexane,methylcyclohexane, ethylcyclohexane, propylcyclohexane,butylcyclohexane, pentylcyclohexane, hexylcyclohexane, dicyclohexyl,heptylcyclohexane, octylcyclohexane, methylisopropylcyclohexane,dimethylcyclohexane, diethylcyclohexane, dipropylcyclohexane,dibutylcyclohexane, dipentylcyclohexane, trimethylcyclohexane,triethylcyclohexane, tetramethylcyclohexane, cyclooctane anddecahydronaphthalene; and aromatic hydrocarbons such as benzene,toluene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene,hexylbenzene, heptylbenzene, octylbenzene, biphenyl, cyclohexylbenzene,cumene, xylene, diethylbenzene, dipropylbenzene, dibutylbenzene,dipentylbenzene, mesitylene, triethylbenzene, tetramethylbenzene,naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthaleneand tetrahydronaphthalene. They may be used alone or in combination oftwo or more. Of these, aromatic hydrocarbons and alicyclic hydrocarbonsare preferred because of their high solubility for catalysts andcopolymers. When the hydrocarbon-based solvent is hydrogenated togetherwith the polymer in the subsequent step (2), alicyclic hydrocarbons arepreferred.

[0054] The polymerization catalyst used in the present invention is notparticularly limited as long as it can copolymerize an α-olefin anddicyclopentadiene. It is preferably a metallocene-based catalyst or aZiegler-based catalyst.

[0055] The metallocene-based catalyst comprises a metallocene and aco-catalyst. The metallocene is preferably represented by the followinggeneral formula (III).

[0056] [In the above formula (III), M is a metal selected from the IVgroup metals, R²⁶ and R²⁷ are the same or different and are each ahydrogen atom, halogen atom, saturated or unsaturated hydrocarbon grouphaving 1 to 12 carbon atoms, alkoxy group having 1 to 12 carbon atoms,or aryloxy group having 6 to 12 carbon atoms, R²⁴ and R²⁵ are the sameor different and are each a monocyclic or polycyclic hydrocarbon groupwhich can form a sandwich structure with a center metal M, and R²³ is abridge for connecting an R²⁴ group and an R²⁵ group and selected from

[0057] (R²⁸ to R³¹ are the same or different and are each a hydrogenatom, halogen atom, saturated or unsaturated hydrocarbon group having 1to 12 carbon atoms, alkoxy group having 1 to 12 carbon atoms or aryloxygroup having 6 to 12 carbon atoms, or R²⁸ and R²⁹ or R³⁰ and R³¹ mayform a ring).]

[0058] In the metallocene represented by the above formula (III), thecenter metal M is the most preferably zirconium from the viewpoint ofcatalytic activity. R²⁶ and R²⁷ may be the same or different but theyare preferably an alkyl group having 1 to 6 carbon atoms or a halogenatom (especially chlorine atom). R²⁴ and R²⁵ are each a cyclichydrocarbon group, as preferably exemplified by a cyclopentadienylgroup, indenyl group or fluorenyl group. They may be substituted by ahydrogen atom, alkyl group such as a methyl group, ethyl group,isopropyl group or tert-butyl group, phenyl group or benzyl group. R²⁸to R³¹ are preferably a hydrogen atom, alkyl group having 1 to 6 carbonatoms or phenyl group. R²³ is preferably a lower alkylene group such asa methylene group, ethylene group or propylene group, alkylidene groupsuch as isopropylidene, substituted alkylene group such asdiphenylmethylene, silylene group, or substituted silylene group such asdimethylsilylene or diphenylsilylene.

[0059] The following compounds can be enumerated as examples of themetallocene containing zirconium as the center metal M:dimethylsilylene-bis(1-indenyl)zirconium dichloride,diphenylsilylene-bis(1-indenyl)zirconium dichloride,dibenzylsilylene-bis(1-indenyl)zirconium dichloride,methylene-bis(1-indenyl)zirconium dichloride,ethylene-bis(1-indenyl)zirconium dichloride,diphenylmethylene-bis(1-indenyl)zirconium dichloride,isopropylidene-bis(1-indenyl)zirconium dichloride,phenylmethylsilylene-bis(1-indenyl)zirconium dichloride,dimethylsilylene-bis-[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,diphenylsilylene-bis[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,dibenzylsilylene-bis[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,methylene-bis[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,ethylene-bis[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,diphenylmethylene-bis[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,isopropylidene-bis[1-(2,4,7-trimethyl)indenyl]zirconium dichloride,phenylmethylsilylene-bis[1-(2,4,7-trimethyl)indenyl]zirconiumdichloride, dimethylsilylene-bis[1-(2,4-dimethyl)indenyl]zirconiumdichloride, diphenylsilylene-bis[1-(2,4-dimethyl)indenyl]zirconiumdichloride, dibenzylsilylene-bis[1-(2,4-dimethyl)indenyl]zirconiumdichloride, methylene-bis[1-(2,4-dimethyl)indenyl]zirconium dichloride,ethylene-bis[1-(2,4-dimethyl)indenyl]zirconium dichloride,diphenylmethylene-bis[1-(2,4-dimethyl)indenyl]zirconium dichloride,isopropylidene-bis[1-(2,4-dimethyl)indenyl]zirconium dichloride,phenylmethylsilylene-bis[1-(2,4-dimethyl)indenyl]zirconium dichloride,dimethylsilylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconium dichloride,diphenylsilylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconium dichloride,dibenzylsilylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconium dichloride,methylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconium dichloride,ethylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconium dichloride,diphenylmethylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconiumdichloride, isopropylidene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconiumdichloride,phenylmethylsilylene-bis[1-(4,5,6,7-tetrahydro)indenyl]zirconiumdichloride, dimethylsilylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride, diphenylsilylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride, dibenzylsilylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride, methylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride, ethylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride, diphenylmethylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride, isopropylidene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride,phenylmethylsilylene-(9-fluorenyl)(cyclopentadienyl)zirconiumdichloride,dimethylsilylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,diphenylsilylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,dibenzylsilylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,methylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,ethylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,diphenylmethylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,isopropylidene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,phenylmethylsilylene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,dimethylsilylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,diphenylsilylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,dibenzylsilylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,methylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,ethylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,diphenylmethylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,isopropylidene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,phenylmethylsilylene-(9-fluorenyl)[1-(3-methyl)cyclopentadienyl]zirconiumdichloride,dimethylsilylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,diphenylsilylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,dibenzylsilylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,methylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,ethylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,diphenylmethylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,isopropylidene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride,phenylmethylsilylene-[9-(2,7-di-tert-butyl)fluorenyl](cyclopentadienyl)zirconiumdichloride, dimethylsilylene-(1-indenyl)(cyclopentadienyl)zirconiumdichloride, diphenylsilylene-(1-indenyl)(cyclopentadienyl)zirconiumdichloride, dibenzylsilylene-(1-indenyl)(cyclopentadienyl)zirconiumdichloride, methylene-(1-indenyl)(cyclopentadienyl)zirconium dichloride,ethylene-(1-indenyl)(cyclopentadienyl)zirconium dichloride,diphenylmethylene-(1-indenyl)(cyclopentadienyl)zirconium dichloride,isopropylidene-(1-indenyl)(cyclopentadienyl)zirconium dichloride,phenylmethylsilylene-(1-indenyl)(cyclopentadienyl)zirconium dichloride,dimethylsilylene-bis(cyclopentadienyl)zirconium dichloride,diphenylsilylene-bis(cyclopentadienyl)zirconium dichloride,dibenzylsilylene-bis(cyclopentadienyl)zirconium dichloride,methylene-bis1(cyclopentadienyl)zirconium dichloride,ethylene-bis(cyclopentadienyl)zirconium dichloride,diphenylmethylene-bis(cyclopentadienyl)zirconium dichloride,isopropylidene-bis(cyclopentadienyl)zirconium dichloride,phenylmethylsilylene-bis(cyclopentadienyl)zirconium dichloride,isopropylidene-(1-indenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,isopropylidene-(9-fluorenyl)[1-(3-isopropyl)cyclopentadienyl]zirconiumdichloride,isopropylidene-[1-(2,4,7-trimethyl)indenyl](cyclopentadienyl)zirconiumdichloride,ethylene-(cyclopentadienyl)[1-(3-tert-butyl)cyclopentadienyl]zirconiumdichloride,ethylene-(cyclopentadienyl)[1-(3-phenyl)cyclopentadienyl]zirconiumdichloride, isopropylidene-(9-fluorenyl)(cyclopentadienyl)zirconiumdibromide, dimethylsilylene-bis(1-indenyl)zirconium dibromide andethylene-bis(1-indenyl)methyl zirconium monochloride.

[0060] In the present invention, particularly preferred metallocenes areisopropylidene-(9-fluorenyl) (cyclopentadienyl)zirconium dichloride,diphenylmethylene- (9-fluorenyl) (cyclopentadienyl)zirconium dichloride,isopropylidene-(9-fluorenyl) [1-(3-methyl)-cyclopentadienyl]zirconiumdichloride, isopropylidene-(9-fluorenyl)[1-(3-tert-butyl)cyclopentadienyl]zirconium dichloride,isopropylidene-(1-indenyl) (cyclopentadienyl)zirconium dichloride,dimethylsilylene-bis(1-indenyl) zirconium dichloride,ethylene-bis(1-indenyl) zirconium dichloride andisopropylidene-bis(1-indenyl)zirconium dichloride.

[0061] The concentration of the metallocene may be determined accordingto its polymerization activity. The metallocene is used in an amount of10⁻⁶ to 10⁻² mol, preferably 10⁻⁵ to 10⁻³ mol, per mol of thedicyclopentadiene added to a polymerization reaction system.

[0062] The co-catalyst is preferably an aluminoxane, which is an organicaluminum oxy compound. The aluminoxane can be represented by the generalformula (IV) when it has a linear structure and by the general formula(V) when it has a cyclic structure.

[0063] [In the formulas (IV) and (V), R³² to R³⁷ are the same ordifferent and are each an alkyl group having 1 to 6 carbon atoms such asa methyl group, ethyl group, propyl group or butyl group, phenyl groupor benzyl group. They are preferably a methyl group or ethyl group andparticularly preferably a methyl group. m is an integer of 2 or more,preferably 5 to 100.]

[0064] However, the accurate structure of the aluminoxane is unknown.

[0065] The aluminoxane can be produced by conventionally known methods,one of which comprises reacting a compound containing absorbed water ora salt containing crystal water (such as copper sulfate hydrate) with anorganic aluminum compound such as trialkyl aluminum in an inert solvent(such as toluene). The aluminoxane may contain a small amount of anorganic aluminum compound derived from the above production methods.

[0066] The aluminoxane serves to alkylate the metallocene and to make itcationic, whereby polymerization activity is obtained. Since theactivation of the metallocene is carried out in a solution, themetallocene is preferably dissolved in an aluminoxane solution. Asolvent used for the activation is preferably an aliphatic hydrocarbon,alicyclic hydrocarbon or aromatic hydrocarbon. Of these, a solventidentical to one used for the polymerization reaction is the mostpreferred. The activation of the metallocene with the aluminoxane iscarried out, normally prior to the polymerization reaction and the timerequired for the activation is 1 minute to 10 hours, preferably 3minutes to 1 hour. The activation is carried out at a temperature of −40to 110° C., preferably 0 to 80° C.

[0067] Although the concentration of the aluminoxane solution is notparticularly limited within the range from 1 wt % to the limit ofdissolution, it is preferably 5 to 30 wt %. The amount of thealuminoxane is 30 to 20,000 mols, preferably 100 to 5,000 mols, per molof the metallocene. If the amount of the aluminoxane is too small,sufficiently high polymerization activity cannot be obtained. On theother hand, when the amount is too large, it is uneconomical because alarge amount of an expensive aluminoxane is used, even though highpolymerization activity can be obtained, and furthermore, purificationafter polymerization becomes difficult disadvantageously.

[0068] A preferred co-catalyst other than aluminoxanes includes an ionicboron compound and an alkylating agent.

[0069] Illustrative examples of the ionic boron compound are compoundsrepresented by the following general formulas (VI) to (IX).

[R³⁸ ₃C]⁺[BR³⁹ ₄]⁻  (VI)

[R³⁸ _(X)NH_(4-X)]⁺[BR³⁹ ₄]⁻  (VII)

[R³⁸ _(X)PH_(4-X)]⁺[BR³⁹ ₄]⁻  (VIII)

Li⁺[BR³⁹ ₄]⁻  (IX)

[0070] [In the above formulas (VI) to (IX), R³⁸s are the same ordifferent and are each an aliphatic hydrocarbon group having 1 to 8carbon atoms or aromatic hydrocarbon group having 6 to 18 carbon atoms.R³⁹s are the same or different and are each an aromatic hydrocarbongroup having 6 to 18 carbon atoms. X is 1, 2, 3 or 4.]

[0071] In the ionic boron compounds represented by the above formulas(VI) to (IX), R³⁸s are each an alkyl group such as a methyl group, ethylgroup, propyl group or butyl group, or an aryl group such as a phenylgroup. R³⁹s are preferably the same and are each a fluorinated orpartially fluorinated aromatic hydrocarbon group, particularlypreferably a pentafluorophenyl group. X is preferably 3. The ionic boroncompounds include, for example,N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate,trityltetrakis(pentafluorophenyl)borate andlithiumtetrakis(pentafluorophenyl)borate.

[0072] The alkylating agent is preferably an alkyl lithium compound oralkyl aluminum compound, as exemplified by methyl lithium, butyllithium, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum andtri-n-butyl aluminum.

[0073] The ionic boron compound serves to make the metallocene cationicand the alkylating agent serves to alkylate the metallocene.Polymerization activity can be obtained by combining these.

[0074] As for the ratio of the ionic boron compound to the metallocene,the ionic boron compound is used in an amount of 0.5 to 10 mols,preferably 0.8 to 3 mols, more preferably 0.9 to 2 mols, per mol of themetallocene. The alkylating agent is used in an amount of 2 to 500 molsper mol of the metallocene. The required amount of the ionic boroncompound based on the metallocene is much smaller and catalytic activitytends to be higher than when an aluminoxane is used as a co-catalyst.Therefore, the amounts of the metallocene and the co-catalyst can bereduced, thereby making it possible to obtain a large economicaladvantage and a large advantage in purification after polymerization.

[0075] In general, these co-catalysts are used directly or prepared as asolution of a hydrocarbon solvent as described above. They can also beused as being supported on a support. The support is preferably aninorganic compound such as silica gel or alumina, or a fine polyolefinpowder such as polyethylene or polypropylene.

[0076] The other preferred polymerization catalyst used in the presentinvention is a Ziegler-based catalyst. The Ziegler-based catalyst usedin the present invention is a catalyst comprising a vanadium compoundand an organic aluminum compound. The vanadium compound is selected fromthe vanadium compounds represented by the following general formulas (X)and (XI) and electron donor adducts thereof.

VO(OR⁴⁰)_(a)R⁴¹ _(b)  (X)

V(OR⁴⁰ )_(c)R⁴¹ _(d)  (XI)

[0077] [In the above formulas (X) and (XI), R⁴⁰s are the same ordifferent and are each an aliphatic hydrocarbon group having 1 to 8carbon atoms or aromatic hydrocarbon group having 6 to 18 carbon atoms.R⁴¹s are the same or different and are each a halogen atom, aliphatichydrocarbon group having 1 to 8 carbon atoms or aromatic hydrocarbongroup having 6 to 18 carbon atoms. a, b, c and d are integers whichsatisfy 0≦a≦3, 0≦b≦3, 2≦a+b≦3, 0≦c≦4, 0≦d≦4 and 3≦c+d≦4.]

[0078] Illustrative examples of the vanadium compound includevanadium(oxy)trichloride, vanadium(oxy) (ethoxy)dichloride,vanadium(oxy)(propoxy)dichloride, vanadium(oxy) (isopropoxy)dichloride,vanadium(oxy)(butoxy)dichloride, vanadium(oxy)(isobutoxy)dichloride,vanadium(oxy)(diethoxy)chloride, vanadium(oxy)(diisopropoxy)chloride,vanadium (oxy)(dibutoxy)chloride, vanadium(oxy)(diisobutoxy)chloride,vanadium(oxy)triethoxide, vanadium(oxy)tripropoxide,vanadium(oxy)triisopropoxide, vanadium(oxy)tributoxide,vanadium(oxy)triisobutoxide, vanadium trichloride, vanadium tribromideand vanadium tetrachloride. Electron donors used to prepare the electrondonor adducts of the vanadium compounds include oxygen-containingelectron donors such as alcohols, phenols, ketones, aldehydes,carboxylic acids, acid esters, acid amides, acid anhydrides, ethers andalkoxysilanes, and nitrogen-containing electron donors such as amines,nitriles and isocyanates.

[0079] The content of the vanadium compound or electron donor adductthereof may be determined according to its polymerization activity. Itis generally 10⁻⁶ to 10⁻² mol, preferably 10⁻⁵ to 10⁻³ mol, per mol ofthe dicyclopentadiene added to the polymerization reaction system.

[0080] The organic aluminum compound contained in the Ziegler-basedcatalyst is a compound having at least one aluminum-carbon bond in themolecule. Illustrative examples of the organic aluminum compound includetrialkyl aluminum compounds such as triethyl aluminum and triisobutylaluminum; organic aluminum alkoxide compounds such as diethyl aluminumethoxide, diisobutyl aluminum butoxide and ethyl aluminumsesquiethoxide; organic aluminum oxy compounds such as methylaluminoxane and ethyl aluminoxane; and organic aluminum halide compoundssuch as diethyl aluminum chloride, diisobutyl aluminum chloride, ethylaluminum sesquichloride, butyl aluminum sesquichloride, ethyl aluminumdichloride and isobutyl aluminum dichloride. Of these, organic aluminumhalide compounds are particularly preferred.

[0081] The organic aluminum compound serves to alkylate a vanadiumcompound or an electron donor adduct thereof, whereby polymerizationactivity is obtained. A solvent used for the activation is preferably analiphatic hydrocarbon, alicyclic hydrocarbon or aromatic hydrocarbon. Ofthese, a solvent identical to one used for the polymerization reactionis the most preferred.

[0082] As for the ratio of the organic aluminum compound to the vanadiumcompound or electron donor adduct thereof, the organic aluminum compoundis used in an amount of 2 to 500 mols, preferably 2 to 50 mols, morepreferably 3 to 30 mols, per mol of the vanadium compound or electrondonor adduct thereof. When the amount of the organic aluminum compoundis too small, high activity cannot be obtained, while when the amount istoo large, the obtained polymer may be gelled disadvantageously.

[0083] Addition copolymerization is carried out at a temperature of −20to 150° C., preferably −10 to 120° C., more preferably 0 to 100° C. Whenthe polymerization temperature is too low, a polymerization reactiondoes not proceed smoothly, while when the polymerization temperature istoo high, the catalyst is deactivated disadvantageously. Thepolymerization temperature is preferably as constant as possible toobtain a homogeneous polymer.

[0084] In order to obtain a copolymer having high chemical homogeneity,the ratio of the α-olefin to dicyclopentadiene is preferably maintainedat least at a predetermined value. As a result, the copolymer solutioninevitably contains unreacted dicyclopentadiene. Reaction conditions arepreferably controlled in such a manner to ensure that the residualamount of the unreacted dicyclopentadiene is 50% or less, preferably 30%or less, more preferably 20% or less of the total amount of the addeddicyclopentadiene.

[0085] The copolymer solution produced by the polymerization reaction issubsequently subjected to a hydrogenation reaction in the presence of ahydrogenation reaction catalyst. The polymerization catalyst containedin the copolymer solution may hinder the activity of the hydrogenationreaction catalyst. In that case, it is preferred to remove thepolymerization catalyst from the copolymer solution as required beforethe hydrogenation reaction.

[0086] The method for removing the polymerization catalyst, though notparticularly limited, is preferably a method which comprises adding anactive hydrogen-containing compound to the copolymer solution toprecipitate a catalyst component and removing it by filtration, a methodwhich comprises washing the copolymer solution with water and extractinga catalyst component in a water phase, or the like. Specific examples ofthe active hydrogen-containing compound include water; alcohols such asmethanol, ethanol and 1-butanol; phenols such as phenol, cresol, xylenoland catechol; carboxylic acids such as formic acid, acetic acid andlactic acid; and amines such as ammonia, ethylamine, n-propylamine,ethylenediamine and monoethanolamine.

[0087] The solution from which the catalyst has been removed may bepurified by bringing it into contact with an adsorbent. The adsorbent ispreferably activated clay, silica gel, alumina, silica alumina orzeolite.

[0088] (step (2))

[0089] The α-olefin-dicyclopentadiene copolymer solution produced in thestep (1) is subjected to a hydrogenation reaction in the presence of ahydrogenation catalyst in the step (2) to hydrogenate unsaturated doublebonds contained in the copolymer, whereby a hydrogenatedα-olefin-dicyclopentadiene copolymer is produced.

[0090] The hydrogenation catalyst used in the present invention is notparticularly limited as long as it is a catalyst generally used for thehydrogenation reaction of an olefin compound. The hydrogenation catalystis preferably a catalyst consisting of a transition metal compound andan alkylating agent, a homogenous noble metal catalyst, or aheterogeneous catalyst.

[0091] The transition metal compound contained in the catalystconsisting of a transition metal compound and an alkylating agent is ahalide, acetylacetonato complex, carboxylate complex, naphthate complex,trifluoroacetate complex, stearate complex or the like of a transitionmetal such as titanium, vanadium, chromium, manganese, iron, ruthenium,cobalt, rhodium, nickel or palladium. Specific examples of thetransition metal compound include bis(cyclopentadienyl)titaniumdichloride, triethyl vanadate, tris(acetylacetonato)chromium,tris(acetylacetonato)manganese, cobalt acetate,tris(acetylacetonato)cobalt, cobalt octenate andbis(acetylacetonato)nickel. The alkylating agent is, for example,lithium, magnesium, aluminum or zinc compound. Specific examples of thealkylating agent include butyl lithium, dimethyl magnesium, triethylaluminum, triisobutyl aluminum, methyl aluminoxane and diethylzinc. Ofthese, a combination of a titanium, cobalt or nickel compound and analkyl aluminum compound or alkyl lithium compound is preferred, and acombination of bis(cyclopentadienyl)titanium dichloride and butyllithium and a combination of tris(acetylacetonato)cobalt orbis(acetylacetonato)nickel and an alkyl aluminum compound such astriethyl aluminum, triisobutyl aluminum or methyl aluminoxane areparticularly preferred from the viewpoint of catalytic activity.

[0092] As for the quantitative relationship between the transition metalcompound and the alkylating agent, the proportion of the metal componentof the alkyl metal compound is 1 to 50 mols, preferably 10 mols or less,per mol of the metal of the transition metal compound.

[0093] The transition metal compound is converted into an alkylatedtransition metal compound by the alkylating agent to have ahydrogenation catalytic activity.

[0094] The homogeneous noble metal catalyst is a catalyst which does notnecessarily require an alkylating agent, as exemplified bycarbonyl(chloro)(hydride)tris(triphenylphosphine)ruthenium,di(hydride)(carbonyl)tris(triphenylphosphine)ruthenium,di(hydride)tetrakis(triphenylphosphine)ruthenium,tetra(hydride)tris(triphenylphosphine)ruthenium,(chloro)tris(triphenylphosphine)rhodium andhydride(carbonyl)tris(triphenylphosphine)rhodium.

[0095] The heterogeneous catalyst is a solid catalyst which has a metalsupported on a support and which is insoluble in a solvent. Illustrativeexamples of the metal include iron, ruthenium, cobalt, rhodium, iridium,nickel, palladium and platinum. Illustrative examples of the supportinclude carbon, silica, alumina, silica aluminum and diatomaceous earth.

[0096] The content of the transition metal compound of the hydrogenationcatalyst may be determined according to its polymerization activity. Itis generally 10⁻⁶ to 10⁻¹ mol, preferably 10⁻⁵ to 10⁻² mol, per mol ofthe double bonds between carbons contained in the polymer.

[0097] The temperature, hydrogen pressure and reaction time of thehydrogenation reaction of the copolymer may be determined according tothe types of monomers used for addition polymerization and the type ofthe hydrogenation catalyst. The temperature is generally 0 to 200° C.,preferably 20 to 180° C., the hydrogen pressure is 0.1 to 200 kgf/cm²,preferably 1 to 150 kgf/cm², and the reaction time is 0.1 to 20 hours.At a low temperature and a low hydrogen pressure, the hydrogenationreaction does not proceed smoothly disadvantageously. At a hightemperature and a high hydrogen pressure, on the other hand, thecatalyst is deactivated and a great load is imposed on equipmentdisadvantageously.

[0098] The degree of hydrogenation of the copolymer (degree ofhydrogenation of the double bonds between carbons) is preferably 99% ormore, more preferably 99.5% or more, much more preferably 99.9% or more.When the degree of hydrogenation is lower than 99%, thermal stabilitybecomes insufficient and discoloration easily occurs at the time of meltmolding. In the case of a ring-opening polymer having double bondsbetween carbons in the main chain, the glass transition temperature ofthe polymer is greatly reduced by hydrogenation. However, in the case ofthe copolymer of the present invention, the double bonds between carbonsare situated in the side chains and, hence, the glass transitiontemperature does not change very much before and after hydrogenation.

[0099] The unreacted dicyclopentadiene monomer contained in theα-olefin-dicyclopentadiene copolymer solution produced in the step (1)is hydrogenated by a hydrogenation catalyst in the step (2) to beconverted into tetrahydrodicyclopentadiene. Since a monomer is generallyhydrogenated more easily than a polymer, dicyclopentadiene issubstantially completely hydrogenated when the degree of hydrogenationof the copolymer is 99% or more. Therefore, the mixture containing thehydrogenated α-olefin-dicyclopentadiene copolymer contains thetetrahydrodicyclopentadiene.

[0100] The polymerization catalyst and/or the hydrogenation catalyst canbe removed from the mixture containing the hydrogenatedα-olefin-dicyclopentadiene copolymer produced in each step after thestep (2) or the step (3). A mixture (2) containing a hydrogenatedα-olefin-dicyclopentadiene copolymer that substantially contains neithermetal derived from the polymerization catalyst nor metal derived fromthe hydrogenation catalyst can be thereby produced.

[0101] When the hydrogenation catalyst is a homogeneous catalyst, themethod for removing the catalyst may be the same as the method forremoving the polymerization catalyst in the step (1). When thehydrogenation catalyst is a heterogeneous catalyst, the catalyst can beseparated from the hydrogenated copolymer solution by filtration. Whenthe hydrogenated copolymer solution from which the heterogeneouscatalyst has been removed contains the polymerization catalyst, thepolymerization catalyst can be removed by the same method as the methodfor removing the polymerization catalyst in the step (1).

[0102] (step (3))

[0103] In the step (3), tetrahydrodicyclopentadiene is distilled offfrom the solution mixture (3) containing the hydrogenatedα-olefin-dicyclopentadiene copolymer.

[0104] In the present invention, at the end of the step (3), at leastone of the following operations (i), (ii) and (iii) must be carried outto ensure that a high-boiling hydrocarbon solvent is existent in anamount of at least 100 parts by weight based on 100 parts by weight ofthe hydrogenated α-olefin-dicyclopentadiene copolymer:

[0105] (i) use of a high-boiling hydrocarbon solvent as at least part ofthe hydrocarbon solvent of the step (1),

[0106] (ii) addition of a high-boiling hydrocarbon solvent in the step(2), and

[0107] (iii) addition of a high-boiling hydrocarbon solvent in the step(3).

[0108] The high-boiling hydrocarbon solvent used herein is a hydrocarbonhaving a boiling point of 195 to 300° C. and an ignition point of 260°C. or more. When the boiling point is lower than 195° C.,tetrahydrodicyclopentadiene cannot be removed efficiently, while theboiling point is higher than 300° C., energy costs for removinghigh-boiling hydrocarbon solvent become too high. When the ignitionpoint is lower than 260° C., the hydrogenated copolymer cannot be heateduntil it is molten, disadvantageously. The high-boiling hydrocarbonsolvent preferably has a melting point of 50° C. or less because apolymerization reaction can be easily carried out in a solution state.The high-boiling hydrocarbon solvent may be existent in an amount of upto 10,000 parts by weight.

[0109] Illustrative examples of the high-boiling hydrocarbon solventinclude alkylbenzene compounds such as pentylbenzene, hexylbenzene,heptylbenzene, octylbenzene, cyclohexylbenzene, dibutylbenzene,dipentylbenzene, 1,3,5-triethylbenzene, 1,2,3,4-tetramethylbenzene and1,2,3,5-tetramethylbenzene; alkylnaphthalene compounds such as1-methylnaphthalene, 2-methylnaphthalene, 1-ethylnaphthalene,2-ethylnaphthalene, 1,2-dimethylnaphthalene, 1,4-dimethylnaphthalene and1,6-dimethylnaphthalene; and tetrahydronaphthalene. Of these,1-methylnaphthalene, 2-methylnaphthalene and tetrahydronaphthalene areparticularly preferred because it is easy to use them industrially. Theymay be used alone or in combination of two or more.

[0110] It is preferable that the high-boiling hydrocarbon solvent becontained in the copolymer solution by carrying out the above operation(i) to eliminate a complicated step in an industrial-scale production,and it is also preferable that the hydrocarbon solvent comprise only thehigh-boiling hydrocarbon solvent. The high-boiling hydrocarbon solventhas a large influence upon neither a copolymerization reaction betweenan α-olefin and dicyclopentadiene nor the hydrogenation reaction of theα-olefin-dicyclopentadiene copolymer. However, when the high-boilinghydrocarbon solvent itself is hydrogenated in the hydrogenation reactionstep (2), the high-boiling hydrocarbon solvent is preferably added tothe solution after the hydrogenation reaction step (2).

[0111] The distill-off of tetrahydrodicyclopentadiene is accomplished byheating the hydrogenated copolymer solution at a temperature higher thanthe boiling point (194° C. at normal pressure) oftetrahydrodicyclopentadiene and lower than the ignition point (235° C.)of tetrahydrodicyclopentadiene. To distill offtetrahydrodicyclopentadiene efficiently, the pressure inside theequipment may be reduced.

[0112] The boiling point of tetrahydrodicyclopentadiene is lower thanthe boiling point of the high-boiling hydrocarbon solvent. Therefore,tetrahydrodicyclopentadiene is distilled off from the hydrogenatedcopolymer solution prior to the high-boiling hydrocarbon solvent. Sincethe solution viscosity of the hydrogenated copolymer solution is muchlower than that of a system where the high-boiling hydrocarbon solventis not present, tetrahydrodicyclopentadiene can be distilled offextremely easily and efficiently. Thus, a hydrogenatedα-olefin-dicyclopentadiene copolymer is produced as a solution in thehigh-boiling hydrocarbon solvent containing substantially notetrahydrodicyclopentadiene.

[0113] A description is subsequently given of the second productionprocess of the present invention.

[0114] As for what is not described of the second production processherein, it should be understood that what has been described of thefirst production process can be applied directly or with somemodifications which are obvious for those skilled in the art.

[0115] The step (1′) is identical to the step (1) of the firstproduction process.

[0116] In the step (2′), unreacted dicyclopentadiene is distilled offfrom the α-olefin-dicyclopentadiene copolymer solution containing theunreacted dicyclopentadiene produced in the step (1′), and anα-olefin-dicyclopentadiene copolymer solution containing substantiallyno unreacted dicyclopentadiene is produced.

[0117] Dicyclopentadiene is distilled off prior to the high-boilinghydrocarbon solvent because its boiling point (170° C. at normalpressure) is lower than the boiling point of the high-boilinghydrocarbon solvent. Since the solution viscosity of theα-olefin-dicyclopentadiene copolymer solution is much lower than that ofa system where the high-boiling hydrocarbon solvent is not present, theunreacted dicyclopentadiene can be distilled off extremely easily andefficiently.

[0118] Dicyclopentadiene undergoes a reverse Diels-Alder reaction and aDiels-Alder reaction and changes into a cyclopentadiene monomer oroligomer when heated to 160° C. The cyclopentadiene oligomer has a highboiling point and it is very difficult to remove it. Therefore, whendicyclopentadiene is to be distilled off, the pressure is preferably setto 600 mmHg or less to prevent the formation of the cyclopentadieneoligomer.

[0119] After the step (2′), the step of removing the polymerizationcatalyst from the α-olefin-dicyclopentadiene copolymer solution can becarried out.

[0120] In the subsequent step (3′), a hydrogenation catalyst is added tothe α-olefin-dicyclopentadiene copolymer solution produced in theprevious step to hydrogenate unsaturated double bonds contained in thecopolymer so as to obtain a mixture containing a hydrogenatedα-olefin-dicyclopentadiene copolymer. The step (3′) is carried out inthe same manner as in the above-described step (2). Since the unreacteddicyclopentadiene is substantially removed in the step (2′),tetrahydrodicyclopentadiene is not substantially contained in themixture containing the hydrogenated α-olefin-dicyclopentadienecopolymer.

[0121] After the step (3′) is carried out, the polymerization catalystand/or the hydrogenation catalyst are/is removed from the mixturecontaining the hydrogenated α-olefin-dicyclopentadiene copolymer toobtain a hydrogenated α-olefin-dicyclopentadiene copolymer solutioncontaining substantially neither metal derived from the polymerizationcatalyst nor metal derived from the hydrogenation catalyst.

[0122] In the second production process, at least one of the followingtwo operations (i′) and (ii′) is carried out to ensure that ahigh-boiling hydrocarbon solvent is existent in an amount of at least100 parts by weight based on 100 parts by weight of theα-olefin-dicyclopentadiene copolymer in the step (2′):

[0123] (i′) use of a high-boiling hydrocarbon solvent as at least partof the hydrocarbon solvent of the step (1′), and

[0124] (ii′) addition of a high-boiling hydrocarbon solvent in the step(2).

[0125] It is preferable that the solvent should be further removed fromthe hydrogenated α-olefin-dicyclopentadiene copolymer obtained by thefirst production process or the second production process of the presentinvention to collect the polymer. The solvent is removed by such anapparatus as a heating vacuum concentrator or vented extruder. Since thecopolymer contains substantially no tetrahydrodicyclopentadiene, it canbe heated to a high temperature higher than 235° C. and lower than theignition point of the solvent.

[0126] Another big feature of the present invention is the simplicity ofthe solvent removal step. Generally speaking, when a solvent is to beremoved from a polymer solution, the temperature of the solution doesnot go beyond the boiling point of the solvent used until the solvent issubstantially completely removed. When the boiling point of the solventused as low as 100° C., a reduction in solution viscosity and anincrease in solubility by heating cannot be expected. As the solvent isremoved, the viscosity rises, a concentration distribution of thesolution is produced, and the polymer precipitated out on the wall of avessel as a solid. Under such a circumstance, it is extremely difficultto stir the solution and the efficient removal of the solvent cannot beexpected. In contrast to this, when a high-boiling hydrocarbon solventis used as in the present invention, solution viscosity can be reducedand solubility can be increased by heating the solution to a hightemperature. As a result, the polymer can be directly molten from asolution state without going through a solid state, thereby making itpossible to remove the solvent very efficiently and substantiallycompletely.

[0127] According to the present invention, a hydrogenatedα-olefin-dicyclopentadiene copolymer containing substantially notetrahydrodicyclopentadiene can be molded by the melt molding method ofthe present invention.

[0128] That is, according to the present invention, there is furtherprovided a method for melt-molding a hydrogenatedα-olefin-dicyclopentadiene copolymer, which comprises the steps ofintroducing a hydrogenated α-olefin-dicyclopentadiene copolymer which areduced viscosity η_(sp)/c, measured at 30° C. in a toluene solutionhaving a concentration of 0.5 g/dl, of 0.25 to 3 dl/g and which isselected from the group consisting of:

[0129] (i) a copolymer comprising recurring units represented by thefollowing formula (A):

[0130] wherein R¹ is a hydrogen atom or a saturated aliphatichydrocarbon group having 1 to 16 carbon atoms, and recurring unitsrepresented by the following formula (B):

[0131] wherein R² is a hydrogen atom or a saturated aliphatichydrocarbon group having 1 to 16 carbon atoms, the molar ratio of therecurring unit (A) to the recurring unit (B) being 0 to 39/100 to 61,and

[0132] (ii) a copolymer comprising recurring units represented by theabove formula (A), recurring units represented by the above formula (B),recurring units represented by the following formula (C):

[0133] wherein n is 0 or 1, m is 0 or a positive integer, p is 0 or 1,R³ to R²² are the same or different and are each a hydrogen atom,halogen atom, aromatic hydrocarbon group having 6 to 10 carbon atoms, orsaturated or unsaturated aliphatic hydrocarbon group having 1 to 12carbon atoms, either R¹⁹ and R²⁰ or R²¹ and R²² may form an alkylidenegroup, and one of R¹⁹ or R²⁰ and one of R²¹ or R²² may form a ring whichmay have a double bond or aromatic ring,

[0134] and recurring units represented by the following formula (D):

[0135] wherein q is an integer of 2 to 8,

[0136] the ratio of the total number of mols of the recurring units (A)and (B) to the total number of mols of the recurring units (C) and (D)being 95 to 99.9/5 to 0.1, the molar ratio of the recurring unit (A) tothe recurring unit (B) being 0 to 39/100 to 61, and the molar ratio ofthe recurring unit (D) to the recurring unit (C) being 0 to 95/100 to 5,into a mold maintained at a temperature range from a temperature 100° C.lower than the glass transition temperature of the copolymer to atemperature 10° C. lower than the glass transition temperature of thecopolymer and molding it at a molten polymer temperature of 230 to 380°C.

[0137] The ratio of the total number of mols of the recurring units (A)and (B) to the total number of mols of the recurring units (C) and (D)is preferably 95 to 98/2 to 5.

[0138] The molar ratio of the recurring unit (A) to the recurring unit(B) is preferably 1 to 38/62 to 99.

[0139] The molar ratio of the recurring unit (D) to the recurring unit(C) is preferably 0 to 80/20 to 100.

[0140] The molecular weight of the above hydrogenatedα-olefin-dicyclopentadiene copolymer is determined in consideration ofmechanical properties and mechanical strength required for an opticalmaterial of interest and resin flowability required for molding. When itis expressed by the reduced viscosity η_(sp)/c measured at 30° C. in atoluene solution having a concentration of 0.5 g/dl, it is in the rangeof 0.25 to 3 dl/g, preferably 0.3 to 2 dl/g, more preferably 0.32 to 1.5dl/g. When the reduced viscosity is lower than 0.25 dl/g, although itsflowability is high and its melting temperature can be thereby reduced,the obtained resin provides a molded product with low mechanicalstrength and is fragile. When the reduced viscosity is higher than 3dl/g, although the mechanical properties of its molded product are high,the melt viscosity of the obtained resin becomes too high, therebymaking melt molding difficult to conduct.

[0141] The molecular weight of the hydrogenated α-olefindicyclopentadiene copolymer can be controlled by supplying apredetermined amount of a molecular weight control agent such ashydrogen or 1-hexene to a polymerization reaction system, by changingthe concentration of a metallocene catalyst, by changing the supply rateof dicyclopentadiene and an α-olefin to the polymerization reactionsystem, or by other methods.

[0142] The glass transition temperature of the hydrogenatedα-olefin-dicyclopentadiene copolymer used in the present invention ispreferably in the range of 100 to 180° C.

[0143] The hydrogenated α-olefin-dicyclopentadiene copolymer used in thepresent invention preferably has a gel content in the resin of 1 wt % orless, more preferably 0.1 wt % or less. The term “gel” as used hereinmeans a residue remaining on a filter when the resin is dissolved intoluene in an amount of 5 wt % and the resulting solution is filteredwith a micro-filter (pore diameter of 1.0 μm). The gel content in theresin can be easily estimated by measuring the weight of the driedresidue.

[0144] When the gel content is more than 1 wt %, a linear streak called“silver streak” or spotted haze called “fish eye” is inevitably formedeven if melt-molding conditions are controlled. In fields which requireprecision molding such as optical disk substrates, the gel content ispreferably 0.1 wt % or less.

[0145] Gels formed in the hydrogenated α-olefin-dicyclopentadienecopolymer can be roughly divided into the following three types:

[0146] (i) gels formed in the polymerization step and derived from apoly-α-olefin typified by polyethylene formed by polymerizing only anα-olefin component or from a copolymer having a large content of anα-olefin component;

[0147] (ii) gels formed by the crosslinking of a double bond portionremaining in the dicyclopentadiene component of theα-olefin-dicyclopentadiene copolymer before hydrogenation; and

[0148] (iii) gels formed by heating and melting in the solvent removalstep or pelletizing step.

[0149] To reduce the amount of these gels as much as possible, forexample, the following methods can be used.

[0150] The gels (i) are formed in the polymerization step. Whenpolymerization is carried out with a relatively large amount ofdicyclopentadiene kept over the α-olefin, gels of this type are hardlyformed. However, when the metallocene catalyst is deactivated byimpurities such as water and oxygen included in the polymerizationsystem, gels of this type may be formed. Therefore, heed must be paid tothe purification of the solvent and monomers, the substitution of theinside of the polymerization system with inert gas, and the like.

[0151] Heed must also be paid to the method of adding the metallocenecatalyst to the polymerization system. The metallocene catalystcomprises a powdery metal complex called “metallocene” and a co-catalystsuch as an aluminum compound, exemplified by methyl aluminoxane (MAO)and triisobutyl aluminum, or an ionic boron compound. Polymerizationactivity is developed only when the both materials react with eachother. They are generally supplied to the polymerization system througha pipe in a solution state. When a catalyst solution, havingpolymerization activity and obtained by reacting a metallocene with aco-catalyst, is supplied, it could happen that the polymerization ofonly an gaseous α-olefin component such as ethylene gas occurs on atrace amount of the catalyst adhered to the inner wall of a pipe andthat the obtained polymer drops into the polymer solution, mixes withthe copolymer and remains as a gel. To prevent this, the solvent isfurther caused to flow to wash the inside of the pipe after the catalystsolution is drained. Preferably, a metallocene solution and aco-catalyst solution are supplied into the polymerization system throughdifferent pipes.

[0152] The gels (ii) can be formed in both the polymerization step andthe hydrogenation step. It is considered that the crosslinking of doublebonds remaining in the dicyclopentadiene component of theα-olefin-dicyclopentadiene copolymer is not caused by the mechanism ofcoordination polymerization such as olefin polymerization in thepresence of a metallocene catalyst but caused by cationic polymerizationmechanism. Therefore, as in the case of the gels (i), preventing theformation of active species for cationic polymerization by removingimpurities such as water and oxygen contained in the polymerizationsystem as much as possible and by suppressing the deactivation of themetallocene catalyst leads to the suppression of gelation caused bycrosslinking.

[0153] Further, the hydrogenation reaction of the polymer solution iscarried out without isolating the α-olefin-dicyclopentadiene copolymerfrom the solution after polymerization. Gelation occurs easily when thecopolymer before hydrogenation is isolated and exposed to the air.Further, when the solution after polymerization is exposed from an inertgas atmosphere to the air, gelation gradually begins to occur.Therefore, it is preferred to carry out a hydrogenation reaction bysupplying the solution after polymerization to an autoclave swiftly withthe solution kept in an inert gas atmosphere and adding a hydrogenationcatalyst. Hydrogenation is preferably carried out within 48 hours, morepreferably 24 hours, after the end of polymerization.

[0154] The gels (iii) are formed in the post-treatment step. Theformation of the gels can be suppressed by using an antioxidant, whichwill be described later, removing the residual catalyst metal componentand carrying out the post-treatment step in a nitrogen atmosphere.

[0155] When a trace amount of gels still remains in the resin even byusing the above methods, the gels can be removed by filtration. The gels(i) and (ii) can be removed by solution filtration and the gels (iii)can be removed by melt filtration.

[0156] The residual catalyst metal component contained in the resincauses coloring, burning or gelation during melt molding. The content ofthe residual catalyst metals in the hydrogenatedα-olefin-dicyclopentadiene copolymer used in the present invention ispreferably 10 ppm or less, more preferably 5 ppm or less. These figuresindicate the total content of all the residual catalyst metals.

[0157] Various methods are conceivable for removing catalyst metals. Wehave already found and proposed an effective method for removingcatalysts efficiently when homogeneous catalysts, such as a metallocenecatalyst, as a polymerization catalyst and a Ziegler-based hydrogenationcatalyst, typified by a combination of tris(acetylacetonato)cobalt orbis(acetylacetonato)nickel and an alkyl aluminum compound, as ahydrogenation catalyst are used (Japanese Patent Applications No.9-283489 and No. 10-81590). According to these applications, a catalystmetal component can be separated and removed by filtration afterprecipitated by adding an oxycarboxylic acid, typified by glycolic acidor lactic acid, and water and optionally a mixture of an activehydrogen-containing compound typified by alcohols, to a solution afterhydrogenation in predetermined amounts based on the total amount ofcatalysts used. When methyl aluminoxane (MAO) or ionic boron compound isused as a co-catalyst for polymerization in the presence of ametallocene catalyst, an alkyl aluminum must be used as an alkylatingagent for the metallocene in large quantities based on the metallocene.Therefore, the removal of aluminum becomes a problem. However, accordingto the purification method, the content of aluminum can be suppressed toan extremely low value at 10 ppm or less.

[0158] The following purification method can be used when a metallocenecatalyst is used as a polymerization catalyst and a heterogeneouscatalyst, having a metal such as palladium, rhodium or nickel supportedon a support such as carbon, alumina or silica alumina, is used as ahydrogenation catalyst. An oxycarboxylic acid, typified by glycolic acidand lactic acid, and water, and optionally a mixture of an activehydrogen-containing compound typified by alcohols, are added to thesolution after polymerization in predetermined amounts based on theamount of the catalyst used to precipitate a metal component derivedfrom the polymerization catalyst and to separate and remove the metalcomponent by filtration. Thereafter, a heterogeneous hydrogenationcatalyst is added to the filtrate to carry out hydrogenation and removedby carrying out filtration again.

[0159] Illustrative examples of the residual metal component containedin the hydrogenated α-olefin-dicyclopentadiene copolymer used in thepresent invention include zirconium, hafnium, titanium, boron andaluminum, all of which are derived from polymerization catalysts, andnickel, cobalt, iron, palladium, rhodium, ruthenium, platinum,manganese, copper, vanadium, magnesium, molybdenum, chromium, zinc andaluminum, all of which are derived from hydrogenation catalysts.

[0160] Low-molecular-weight volatile components, which are generallycontained in the resin, cause the rough surface of a molded product suchas silver streaks or microvoids during melt molding in many cases. Asthe synthesis of the hydrogenated α-olefin-dicyclopentadiene copolymerused in the present invention is generally carried out using ahydrocarbon solvent, the hydrocarbon volatile component is derived fromthe solvent. Illustrative examples of the hydrocarbon volatile componentinclude aliphatic hydrocarbons such as pentane, hexane, octane anddecane; alicyclic hydrocarbons such as cyclopentane, cyclohexane andcyclooctane; and aromatic hydrocarbons such as benzene, toluene andxylene. Of these, aromatic hydrocarbons are commonly used and tolueneand cyclohexane are particularly commonly used.

[0161] The hydrocarbon-based volatile component other than the above istetrahydrodicyclopentadiene. Tetrahydrodicyclopentadiene is formed byhydrogenating dicyclopentadiene, which is a monomer. Two reactions,polymerization and hydrogenation, are required for the synthesis of thehydrogenated α-olefin-dicyclopentadiene copolymer. Preferably,hydrogenation is carried out in succession to polymerization withoutisolating the polymer from the solution from an economical point of viewand the viewpoint of suppressing the gelation of the obtained copolymer.

[0162] According to the first production process and the secondproduction process of the present invention, as described above, thehydrogenated α-olefin-dicyclopentadiene copolymer containingsubstantially no tetrahydrodicyclopentadiene is obtained.

[0163] In the molding of the present invention, a resin is preferablyused that has a total content of these hydrocarbon-based volatilecomponents of 0.1 wt % or less. When the hydrocarbon-based volatilecomponents remain in a total amount of more than 0.1 wt %, it cannot behardly suppressed to roughen the surface during molding.

[0164] A cyclic olefin resin has a large number of tertiary carbons inits structure. Therefore, when it contacts oxygen at a high temperature,it deteriorates by oxidation to form gels and decomposed products,whereby the discoloration, burning or silver streak of a molded producteasily occurs. In the melt molding method of the present invention,these can be suppressed effectively by adding an antioxidant such as aphenol-based compound or phosphorus-based compound to the resin in anamount of preferably 0.01 to 3 wt %, more preferably 0.01 to 1 wt %.When the amount of the antioxidant is smaller than 0.01 wt %, thesuppression effect may be insufficient. On the other hand, when theamount is larger than 3 wt %, silver streaks, a hazy molded product, orstains on the surface of the molded product and the mold are readilyproduced by the vaporization or decomposition of the antioxidant.

[0165] As the antioxidant used herein may be a commonly knowngeneral-purpose antioxidant such as Irganox 1010 or Irganox 1076 (ofCiba Geigy). Phenol-based antioxidants include, for example,2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol, 4-t-butylphenol,2,4-dimethyl-6-t-butylphenol, 4,4′-bis(2,6-di-t-butylphenol),2,2′-methylene-bis(4-methyl-6-t-butylphenol),4,4′-methylene-bis(2,6-di-t-butylphenol),2,2′-dioxy-3,3′-di-t-butyl-5,5′-dimethyldiphenylmethane,tetrakis[2-(3,5-di-t-butyl-4-hydroxyphenyl)ethylpropionate]methane,pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate,tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate,octadecyl-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2,2′-thio-bis-(4-methyl-6-t-butylphenol) and2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate].

[0166] Phosphorus-based antioxidants include, for example,tris(2,4-di-t-butylphenyl)phosphite,bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite,tris(nonylphenyl)phosphite and 3,5-di-t-butyl-4-hydroxybenzylphosphonate diethyl ester.

[0167] They may be used alone or in combination of two or more. Aphenol-based antioxidant may be mixed with a phosphorus-basedantioxidant.

[0168] In the above-described purification method which comprisesremoving the catalyst components by filtration and distilling off thesolvent, the gelation and deterioration of the resin during the removalof the solvent at a high temperature can be suppressed by adding theseantioxidants to the solution after filtration.

[0169] Various additives other than the above antioxidants may be addedto the hydrogenated α-olefin-dicyclopentadiene copolymer used in thepresent invention as required. The additives include an ultravioletabsorber, bluing agent for reducing the yellowness of a molded product,release agent, antistatic agent and glass fibers. These additivespreferably have a large molecular weight to prevent vaporization andelution at the time of molding and are used in as small an amount aspossible to prevent a reduction in transparency.

[0170] To melt-mold the resin, it is dried first. In the presentinvention, it is preferred to dry the resin in advance. To suppressdeterioration by oxidation, vacuum drying or drying in a nitrogen gasstream is particularly preferably carried out to remove oxygen containedin the resin.

[0171] In the melt molding of the present invention, melt molding suchas injection molding or melt extrusion is carried out using thehydrogenated α-olefin-dicyclopentadiene copolymer at a meltingtemperature of 230 to 380° C. and a mold temperature of (Tg−100) to(Tg−10)°C. “Tg” used herein is the glass transition temperature of thehydrogenated α-olefin-dicyclopentadiene copolymer. Outside the aboverange, a molded product having satisfactory characteristic properties isdifficult to obtain.

[0172] When the melting temperature is below 230° C., the flowability ofthe resin becomes insufficient and the distortion of the obtained moldedproduct becomes large disadvantageously. On the other hand, when themelting temperature is above 380° C., the discoloration, decompositionand burning of the molded product readily occur. The melting temperatureis preferably in the range of 250 to 370° C. For molding an optical disksubstrate, it is important to increase the flowability of the resin andit is preferable to mold the optical disk substrate at a temperature of280 to 370° C.

[0173] When the mold temperature is below (Tg−100)° C., the distortionof the molded product becomes large and pit replicability which isrequired in an optical disk substrate deteriorates. On the other hand,when the mold temperature is above (Tg−10)° C., the molded product iseasily deformed or warped while removed from the mold since the moldtemperature is close to the glass transition temperature of thehydrogenated α-olefin-dicyclopentadiene copolymer used.

[0174] The optimum melting temperature, the optimum mold temperature andthe optimum molecular weight of the above hydrogenatedα-olefin-dicyclopentadiene copolymer are selected from the above rangesin consideration of various factors such as the moldability, opticalproperties, mechanical properties and economy of the obtained product.

[0175] Although the melt molding of the present invention can be carriedout in the air atmosphere, it is preferred to carry out melt molding ina nitrogen atmosphere in order to suppress the coloring and gelation ofthe molded product which are caused by deterioration by oxidation. Inthis case, the supply of the resin to a molding machine is carried outin a nitrogen gas atmosphere.

[0176] According to the present invention, optical materials typified byoptical disk substrates, optical lenses and optical sheets havingexcellent optical properties, moldability and mechanical properties canbe molded from the hydrogenated α-olefin-dicyclopentadiene copolymer. Asingle metal layer or multiple metal lagers may be formed on thesurfaces of the obtained optical materials by deposition or sputteringaccording to application purpose. An organic layer such as a protectivelayer or gas barrier layer may also be formed by coating.

[0177] The following examples are provided for the purpose of furtherillustrating the present invention but are in no way to be taken aslimiting.

[0178] In Examples 1 to 3, procedures were carried out in an inertatmosphere such as argon or nitrogen unless otherwise stated.

[0179] Toluene, cyclohexane, tetrahydronaphthalene and dicyclopentadienewere all purified by distillation and fully dried in accordance with acommonly used method before used.

[0180] Isopropylidene-(9-fluorenyl)(cyclopentadienyl) zirconiumdichloride was purchased from Boulder Scientific Co., Ltd. as themetallocene and used without further purification.

[0181] Trityl-tetrakis(pentafluorophenyl)borate was purchased from TosoAkzo Co., Ltd. as the ionic boron compound and used without furtherpurification.

[0182] Polymethyl aluminoxane (PMAO) was purchased from Toso Akzo Co.,Ltd. as the aluminoxane and a 2M toluene solution of PMAO was preparedand used.

[0183] Triisobutyl aluminum was purchased from Toso Akzo Co., Ltd. andused without further purification.

[0184] Tris(acetylacetonato)cobalt was purchased from Wako Pure ChemicalIndustries, Ltd. and used without further purification.

[0185]Pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate](Irganox 1010) was purchased from Tokyo Kasei Kogyo Co., Ltd. and usedwithout further purification.

[0186] Nickel silica alumina was purchased from Aldrich Co., Ltd.

[0187] Measurement items were measured in accordance with the followingmethods. solution viscosity: measured using a BH viscometer of TokyoKeiki Co., Ltd. glass transition temperature (Tg (° C.)): measured at atemperature elevation rate of 20° C./min using the 2920 DSC of TAInstruments Co., Ltd.

[0188] molecular weight: The reduced viscosity η_(sp)/c (dl/g) at 30° C.of a toluene solution having a concentration of 0.5 g/dl was measured.

[0189] composition of solution: The composition of a solution excludinga polymer was measured using a GC-9A gas chromatograph of ShimadzuCorporation. degree of hydrogenation: determined by ¹H-NMR using aJNM-A-400 Nuclear Magnetic Resonance spectrometer of JEOL Ltd.

[0190] content of gel component in resin: The resin is dissolved intoluene to prepare a 5 wt % solution, the solution is filtered with amembrane filter having a pore diameter of 1 μm, and the weight of theresidue remaining on the filter after the filter is dried is measured tocalculate the content.

[0191] amount of residual metal in resin: determined by ICP emissionspectral analysis

[0192] total light transmittance: measured using a UV-240spectrophotometer for ultraviolet and visible region of ShimadzuCorporation.

[0193] coloring of molded product: b value is measured with a CR-200color difference meter of Minolta Camera Co., Ltd. and discoloration isestimated based on the difference in b-value between the molded productand that of a white calibration plate (b=+2.62).

[0194] observation of surface of molded product (disk substrate):measured using a SFA-300 Atomic Force Microscope of Seiko InstrumentsInc.

[0195] birefringence of disk substrate: measured with a single pass at awavelength of 633 nm using the ADR-200B birefringence instrument of OrkSeisakusho Co., Ltd.

REFERENCE EXAMPLE 1

[0196] The temperature-dependency and solution-concentration-dependencyof the solution viscosity of a hydrogenated ethylene-dicyclopentadienecopolymer having a glass transition temperature of 148° C. and a reducedviscosity of 0.40 dl/g were examined. Toluene and tetrahydronaphthalenewere used as solvents. The results are shown in FIG. 1 and FIG. 2. Therelationship between the solution concentration and the solutionviscosity of each of a toluene solution of a hydrogenatedethylene-dicyclopentadiene copolymer at 110° C. and atetrahydronaphthalene solution of the hydrogenated copolymer at 208° C.was derived from these results. The results are shown in FIG. 3.

[0197] Letters A to L in FIGS. 1 to 3 indicate the following.

[0198] A: a straight line showing the relationship between the solutionviscosity and temperature of a 17 wt % toluene solution of thehydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 110° C.

[0199] B: a straight line showing the relationship between the solutionviscosity and temperature of a 30 wt % toluene solution of thehydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 110° C.

[0200] C: a straight line showing the relationship between the solutionviscosity and temperature of a 40 wt % toluene solution of thehydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 110° C.

[0201] D: a straight line showing the relationship between the solutionviscosity and temperature of a 50 wt % toluene solution of thehydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 110° C.

[0202] E: a straight line showing the relationship between the solutionviscosity and temperature of a 17 wt % tetrahydronaphthalene solution ofthe hydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 208° C.

[0203] F: a straight line showing the relationship between the solutionviscosity and temperature of a 30 wt % tetrahydronaphthalene solution ofthe hydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 208° C.

[0204] G: a straight line showing the relationship between the solutionviscosity and temperature of a 40 wt % tetrahydronaphthalene solution ofthe hydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 208° C.

[0205] H: a straight line showing the relationship between the solutionviscosity and temperature of a 60 wt % tetrahydronaphthalene solution ofthe hydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 208° C.

[0206] I: a straight line showing the relationship between the solutionviscosity and temperature of a 80 wt % tetrahydronaphthalene solution ofthe hydrogenated α-olefin-dicyclopentadiene copolymer. White symbolsindicate actual measurement values and black symbols indicateextrapolation values at 208° C.

[0207] J: a straight line showing the relationship between the solutionviscosity and solution concentration at 110° C. of a toluene solution ofthe hydrogenated α-olefin-dicyclopentadiene copolymer obtained from FIG.1.

[0208] K: a straight line showing the relationship between the solutionviscosity and solution concentration at 208° C. of atetrahydronaphthalene solution of the hydrogenatedα-olefin-dicyclopentadiene copolymer obtained from FIG. 2.

[0209] L: a point where a solid begins to precipitate out of a toluenesolution of the hydrogenated α-olefin-dicyclopentadiene copolymer at110° C.

EXAMPLE 1

[0210] There were charged 343 g (2.6 mols) of dicyclopentadiene, 1,320 gof tetrahydronaphthalene and 36 g of triisobutyl aluminum into a 3-literautoclave. The autoclave was pressurized with ethylene having a pressureof 1.5 atm, a tetrahydronaphthalene solution containing 124 mg (0.29mmol) of isopropylidene-(9-fluorenyl) (cyclopentadienyl)zirconiumdichloride and 3 g of triisobutyl aluminum and a tetrahydronaphthalenesolution containing 250 mg (0.27 mmol) oftrityltetrakis(pentafluorophenyl)borate were added, and polymerizationwas carried out at 30° C. Ethylene having a pressure of 1.5 atm wasconstantly supplied during the polymerization, and the supply ofethylene was stopped when 2.34 mols of ethylene was consumed to obtain apolymer solution. The obtained ethylene-dicyclopentadiene copolymer hada Tg of 153° C. and a reduced viscosity of 0.77 dl/g, and the molarfraction of dicyclopentadiene in the copolymer was 46%.

[0211] The copolymer solution was transferred to a 5-liter autoclave,and a tetrahydronaphthalene solution containing 3.0 g (8.4 mmols) oftris(acetylacetonato)cobalt and 4.8 g of triisobutyl aluminum was added.The autoclave was pressurized with hydrogen having a pressure of 40 atm,and a hydrogenation reaction was carried out at 110° C. for 3 hours toobtain a hydrogenated ethylene-dicyclopentadiene copolymer solution. Theobtained hydrogenated copolymer had a Tg of 153° C., a reduced viscosityof 0.47 dl/g and a degree of hydrogenation of 99.9% or more.

[0212] To the hydrogenated copolymer solution were added 21 g of lacticacid and 2.7 g of water. A reaction was carried out at 95° C. for 2hours, and the polymerization catalyst and the hydrogenation catalystwere precipitated. The solution mixture was filtered with Celite toobtain a hydrogenated ethylene-dicyclopentadiene copolymer solutioncontaining substantially no catalyst residue. The solution contained 430parts by weight of tetrahydronaphthalene and 28 parts by weight oftetrahydrodicyclopentadiene based on 100 parts by weight of thehydrogenated ethylene-dicyclopentadiene copolymer. The number of partsby weight of each volatile component based on 100 parts by weight of thecopolymer or the hydrogenated copolymer is expressed by phr hereinafter.

[0213] There was charged 250 g of the obtained hydrogenated copolymersolution into a 500-ml flask, and 125 mg of the Irganox 1010 as anantioxidant was also added to remove volatile components at normalpressure. The temperature of the solution was 205 to 208° C. Thecomposition of the solution was analyzed and tetrahydrodicyclopentadienewas no longer detected when the amount of tetrahydronaphthalene reached56 phr. FIG. 4 shows changes in the composition of the solution. Thesolution viscosity at this point was estimated to be 1,000 cps from FIG.3. The volatile components were continued to be removed by elevating thetemperature of the solution to 300° C. to obtain the hydrogenatedcopolymer in a molten state. During the removal, the solid hydrogenatedpolymer did not precipitate out of the solution.

[0214] Letters M and N in FIG. 4 indicate the following.

[0215] M: a curve showing change of time in the concentration oftetrahydrodicyclopentadiene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 1

[0216] N: a curve showing change of time in the concentration oftetrahydronaphthalene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 1

COMPARATIVE EXAMPLE 1

[0217] A polymerization reaction, hydrogenation reaction, catalystdeposition reaction and catalyst removal operation were carried out inthe same manner as in Example 1 to obtain a hydrogenatedethylene-dicyclopentadiene copolymer solution except that toluene wasused as a solvent and that ethylene was pressurized at 1 atm. Beforehydrogenation, the copolymer had a Tg of 150° C. and an η_(sp)/c of0.67, and the molar fraction of dicyclopentadiene in the copolymer was45%. The hydrogenated copolymer had a Tg of 147° C., a reduced viscosityof 0.43 and a degree of hydrogenation of 99.9% or more. The solutioncontained 430 phr of toluene and 28 phr of tetrahydrodicyclopentadiene.

[0218] There was charged 250 g of the obtained hydrogenated copolymersolution into a 500-ml flask, and 125 mg of Irganox 1010 as anantioxidant was also added to remove volatile components at normalpressure. The temperature of the solution was 110 to 115° C. untiltoluene was almost completely removed. The composition of the solutionwas analyzed during this removal. FIG. 5 shows changes in composition.Toluene was distilled off first, and most of tetrahydrodicyclopentadienewas then distilled off. The solution viscosity sharply increased as theconcentration of the copolymer increased, and the copolymer precipitatedout on the wall of the flask as a solid after the concentration of thecopolymer exceeded 70%. The solution viscosity at this point wasestimated to be 25,000 cps from FIG. 1 and tetrahydrodicyclopentadieneremained in the copolymer in an amount of 20 phr. Toluene was almostremoved as heating was further continued, and the copolymer precipitatedout and, at the same time, the temperature rose. Althoughtetrahydrodicyclopentadiene was distilled off for 2 hours after thetemperature was elevated to 225° C, the copolymer was not molten yet andtetrahydrodicyclopentadiene could not be distilled off completely.Tetrahydrodicyclopentadiene remained in the copolymer in an amount of 10phr.

[0219] Letters O and P in FIG. 5 indicate the following.

[0220] O: a curve showing change of time in the concentration oftetrahydrodicyclopentadiene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in ComparativeExample 1

[0221] P: a curve showing change of time in the concentration of toluenecontained in the hydrogenated α-olefin-dicyclopentadiene copolymersolution obtained in Comparative Example 1

EXAMPLE 2

[0222] A polymerization reaction was carried out in the same manner asin Example 1 except that cyclohexane was used as a solvent and thatethylene was pressurized at 2 atm. The copolymer had a Tg of 147° C. andan η_(sp)/c of 0.64, and the molar fraction of dicyclopentadiene in thecopolymer was 46%. There were added 11 g of lactic acid and 1.4 g ofwater to the obtained polymer solution, and the resulting solution wasallowed to react for 2 hours to precipitate the polymerization catalyst.The obtained polymer solution mixture was filtered with Celite and thefiltrate was transferred to a 5-liter autoclave. Thirty grams of nickelsilica alumina was added to the autoclave as a hydrogenation catalystand the autoclave was pressurized with hydrogen having a pressure of 100atm to carry out a hydrogenation reaction at 150° C. The hydrogenationcatalyst was removed from the obtained hydrogenated copolymer solutionmixture with Celite to obtain a hydrogenated ethylene-dicyclopentadienecopolymer solution. The hydrogenated copolymer had a Tg of 144° C., areduced viscosity of 0.41 and a degree of hydrogenation of 99.9% ormore. The solution contained 420 phr of cyclohexane and 26 phr oftetrahydrodicyclopentadiene.

[0223] There were charged 250 g of the obtained hydrogenated copolymersolution into a 1-liter flask, 69 g (150 phr based on the hydrogenatedcopolymer) of tetrahydronaphthalene, and 125 mg of Irganox 1010 as anantioxidant, to remove volatile components at normal temperature. Thetemperature of the solution was 90 to 210° C. and the composition of thesolution was analyzed during the removal. FIG. 6 shows changes incomposition. Tetrahydrodicyclopentadiene was no longer detected in thesolution when the concentration of tetrahydronaphthalene reached 45 phrbased on the hydrogenated copolymer. The solution viscosity at thispoint was estimated to be 2,000 cps from FIG. 1. The volatile componentswere further removed as the solution temperature was elevated to 300° C.to obtain the hydrogenated copolymer in a molten state. During thisremoval, the solid hydrogenated copolymer did not precipitate out of thesolution.

[0224] Letters Q, R and S in FIG. 6 indicate the following.

[0225] Q: a curve showing change of time in the concentration oftetrahydrodicyclopentadiene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 2

[0226] R: a curve showing change of time in the concentration ofcyclohexane contained in the hydrogenated α-olefin-dicyclopentadienecopolymer solution obtained in Example 2

[0227] S: a curve showing change of time in the concentration oftetrahydronaphthalene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 2

EXAMPLE 3

[0228] A polymerization reaction was carried out using a flask in thesame manner as in Example 1 to obtain an ethylene-dicyclopentadienecopolymer solution except that everything used in Example 1 was scaleddown to {fraction (1/7)}. The copolymer had a Tg of 143° C. and anη_(sp)/c of 0.59, and the molar fraction of dicyclopentadiene in thecopolymer was 43%. The solution contained 400 phr oftetrahydronaphthalene and 30 phr of dicyclopentadiene. The pressure ofthe flask was reduced to 50 mmHg to remove volatile components at 70° C.The composition of the solution was analyzed during this anddicyclopentadiene was no longer detected in the solution when the amountof tetrahydronaphthalene reached 270 phr. FIG. 7 shows changes in thecomposition of the solution. The solution viscosity at this point wasestimated to be 300 cps from FIG. 2.

[0229] Sixty grams of tetrahydronaphthalene was added to the obtainedcopolymer solution. The resulting solution was transferred to a 1-literautoclave, and a tetrahydronaphthalene solution containing 0.4 g (1.1mmols) of tris(acetylacetonato)cobalt and 0.7 g of triisobutyl aluminumwas added. The autoclave was pressurized with hydrogen having a pressureof 40 atm and a hydrogenation reaction was carried out at 110° C. for 3hours to obtain a hydrogenated ethylene-dicyclopentadiene copolymersolution. The obtained hydrogenated copolymer had a Tg of 143° C. and areduced viscosity of 0.42 dl/g.

[0230] Three grams of lactic acid and 0.4 g of water were added to thehydrogenated copolymer solution. The resulting solution was allowed toreact at 95° C. for 2 hours to precipitate the polymerization catalystand the hydrogenation catalyst. The solution mixture was filtered withCelite to obtain a hydrogenated ethylene-dicyclopentadiene copolymersolution containing substantially neither tetrahydrodicyclopentadienenor catalyst residue.

[0231] The hydrogenated copolymer solution was charged into a 500-mlflask, and 125 mg of Irganox 1010 was also added to the flask as anantioxidant. Volatile components were further removed at normal pressureas the temperature of the solution was elevated to 300° C. to obtain thehydrogenated copolymer in a molten state. During the removal, the solidhydrogenated copolymer did not precipitate out of the solution.

[0232] Letters T and U in FIG. 7 indicate the following.

[0233] T: a curve showing change of time in the concentration ofdicyclopentadiene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 3

[0234] U: a curve showing change of time in the concentration oftetrahydronaphthalene contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer solution obtained in Example 3

REFERENCE EXAMPLE 2

[0235] The inside of a 3-liter stainless steel polymerization reactorwas substituted with nitrogen, and 181 g of dicyclopentadiene, 1,150 gof toluene and 3.4 g of triisobutyl aluminum were added to the reactor.After the inside of the reactor was substituted with ethylene havingnormal pressure, a metallocene solution, obtained by dissolving 122 mgof isopropylene(9-fluorenyl)(cyclopentadienyl)zirconium dichloride and0.2 g of triisobutyl aluminum in 85 g of toluene, and a co-catalystsolution, obtained by dissolving 267 mg oftrityl-tetrakis(pentafluorophenyl)borate in 85 g of toluene, weredivided into three portions, which were added to a polymerization systemseparately at intervals of 20 minutes to carry out polymerization at 30°C. During the polymerization, ethylene having normal pressure wasconstantly supplied, and 157 g of dicyclopentadiene was added at such arate that ensures the addition rate of dicyclopentadiene and theconsumption rate of ethylene should become 42:58. The supply of ethylenewas stopped to terminate the reaction when the consumption of ethylenereached 90% of a molar amount equivalent to 338 g of the addeddicyclopentadiene (110 minutes after the first addition of the catalystsolution).

[0236] The obtained polymerization reaction solution was immediatelysupplied to a 5-liter autoclave in a nitrogen atmosphere, and ahydrogenation catalyst solution, prepared by reacting 3.0 g oftris(acetylacetonato)cobalt with 4.8 g of triisobutyl aluminum in 20 mlof toluene in a nitrogen atmosphere at room temperature for 5 minutes,was added the autoclave. Thereafter, a hydrogenation reaction wascarried out at a hydrogen pressure of 30 atm and a temperature of 110°C. for 150 minutes.

[0237] After the solution resulting from the hydrogenation reaction wascooled to 95° C., an aqueous solution of 20.5 g of lactic acid in 2.7 gof water was added dropwise to the solution under agitation in anitrogen atmosphere over 10 minutes to carry out a reaction at 95° C.for another 2 hours. The reaction solution changed from black brown to aturbid pink slurry. The slurry was then filtered. A filter (NaslonNF-05) having a pore diameter of 5 μm was set up in a 11-cm-diametercylindrical filtering device, and 5 cm of Celite and a flannel fabricwere placed on the filter in this order to carry out pressurefiltration. Filtration proceeded smoothly. The obtained filtrate wassubjected to an adsorption treatment using basic alumina to obtain anachromatic transparent resin solution.

[0238] Tetrahydronaphthalene andpentaerythrityltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]was added to this solution in an amount of 150 wt % and 0.2 wt % basedon the hydrogenated copolymer, respectively, and then the solvent andtetrahydrodicyclopentadiene were distilled off. Toluene was distilledoff at normal pressure at first, the temperature was raised gradually to280° C., and distillation was continued until volatile components couldnot be identified at a reduced pressure. Thereafter, the molten resinwas supplied to an extruder in a nitrogen atmosphere to obtain anachromatic transparent pellet. When the pellet was examined, it had areduced viscosity η_(sp)/c, at 30° C. in a toluene solution having aconcentration of 0.5 g/dl, of 0.40 dl/g, a glass transition temperatureof 147° C. and a degree of hydrogenation of 99.9% or more (double bondsignals were not observed when measured by ¹H-NMR). When the amounts ofresidual metals were determined by ICP emission spectral analysis, Zrwas contained in an amount of 0.1 ppm or less, B in an amount of 0.1 ppmor less, Co in an amount of 0.7 ppm, and Al in an amount of 1.8 ppm.When a gel component contained in the pellet was examined by filtering a5 wt % toluene solution prepared by re-dissolving the pellet in toluenewith a micro-filter having a pore diameter of 1 μm, the gel componentwas contained in an amount of 0.01 wt % or less. Further, when thecontent of hydrocarbon-based volatile components contained in the pelletwas measured by gas chromatography (GC), toluene,tetrahydrodicyclopentadiene and tetrahydronaphthalene were not detected.Thus, it was found that most of the hydrocarbon-based volatilecomponents were distilled off.

REFERENCE EXAMPLE 3

[0239] The pellet of a hydrogenated ethylene-dicyclopentadiene copolymerwas obtained in the same manner as in Reference Example 2 except that ametallocene solution and a co-catalyst solution were divided into 5portions, which were added to a polymerization reaction systemseparately at intervals of 20 minutes, and that a polymerizationreaction was terminated 180 minutes after the first addition of thecatalyst solutions. When the pellet was examined in the same manner asin Reference Example 2, it had a reduced viscosity η_(sp)/C of 0.55 dl/g(toluene solution having a concentration of 0.5 g/dl, 30° C.), a glasstransition temperature of 145° C. and a degree of hydrogenation of 99.9%or more (double bond signals were not observed when measured by ¹H-NMR).As for the amounts of residual metals, Zr was contained in an amount of0.1 ppm or less, B in an amount of 0.1 ppm or less, Co in an amount of0.6 ppm, and Al in an amount of 1.6 ppm. The content of the gel in thepellet was 0.01 wt % or less, and toluene, tetrahydrodicyclopentadieneand tetrahydronaphthalene were not observed in the pellet by GC. Thus,it was found that most of the hydrocarbon-based volatile components weredistilled off.

REFERENCE EXAMPLE 4

[0240] The pellet of a hydrogenated ethylene-dicyclopentadiene copolymerwas obtained in the same manner as in Reference Example 2 except thatthe reaction temperature at the time of polymerization was 60° C. Whenthe pellet was examined in the same manner as in Reference Example 2, ithad a reduced viscosity η_(sp)/c of 0.22 dl/g (toluene solution having aconcentration of 0.5 g/dl, 30° C.), a glass transition temperature of149° C., and a degree of hydrogenation of 99.9% or more (double bondsignals were not observed when measured by ¹H-NMR). As for the amountsof residual metals, Zr was contained in an amount of 0.1 ppm or less, Bin an amount of 0.1 ppm or less, Co in an amount of 0.5 ppm, and Al inan amount of 0.9 ppm. The content of the gel in the pellet was 0.01 wt %or less, and toluene and tetrahydrodicyclopentadiene were not observedin the pellet by GC. Thus, it was found that most of thehydrocarbon-based volatile components were distilled off.

REFERENCE EXAMPLE 5

[0241] After polymerization and hydrogenation were carried out in thesame manner as in Reference Example 2, 20 ml of methanol was addeddropwise to a hydrogenation reaction solution cooled to roomtemperature. The resulting solution was ejected into a large amount of amixed solution of acetone and methanol to form a precipitate. Theprecipitate was separated by filtration, washed with acetone, methanoland water, and dried to obtain white powder.Pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]was added to the powder in an amount of 0.2 wt %, and the resultingmixture was hot-pressed at 220° C. to obtain a plate-like product, whichwas then crushed with a crusher to obtain a block of a hydrogenatedethylene-dicyclopentadiene copolymer. This block resin had a reducedviscosity η_(sp)/c of 0.40 dl/g (toluene solution having a concentrationof 0.5 g/dl, 30° C.), a glass transition temperature of 147° C., and adegree of hydrogenation of 99.9% or more (double bond signals were notobserved when measured by ¹H-NMR) as in Reference Example 2. However,the amounts of residual metals were very large with 8 ppm of Zr, 7 ppmof B, 24 ppm of Co and 142 ppm of Al. The content of the gel in theblock was 0.01 wt % or less, and toluene and tetrahydrodicyclopentadienewere not observed in the block by GC. Thus, it was found that most ofthe hydrocarbon-based volatile components were distilled off.

REFERENCE EXAMPLE 6

[0242] After polymerization was carried out in the same manner as inReference Example 2, the polymer solution was left to stand in the airfor 16 hours. Thereafter, a hydrogenation reaction was carried out, andthe same post-treatment as in Reference Example 2 was conducted. Lacticacid and water were added to carry out a reaction, and the reactionsolution was filtered. However, filterability was extremely low, so thata filtrate was obtained by exchanging a filter, Celite and flanneltwice. Thereafter, a pellet was obtained in the same manner as inReference Example 2. The pellet had a reduced viscosity η_(sp)/c of 0.45dl/g (toluene solution having a concentration of 0.5 g/dl, 30° C.), aglass transition temperature of 149° C., and a degree of hydrogenationof 99.9% or more (double bond signals were not observed when measured by¹H-NMR). The amounts of residual metals were very small with 0.1 ppm orless of Zr, 0.1 ppm or less of B, 0.6 ppm of Co and 1.6 ppm of Al.However, the content of the gel in the pellet was large at 1.3 wt %.Toluene, tetrahydrodicyclopentadiene and tetrahydronaphthalene were notobserved in the pellet by GC. Thus, it was found that most of thehydrocarbon-based volatile components were distilled off.

EXAMPLE 4

[0243] Injection molding was carried out with an injection moldingmachine using the pellet of the hydrogenated ethylene-dicyclopentadienecopolymer obtained in Reference Example 2. The melting temperature ofthe resin in the cylinder was set to 280° C. and the temperature of themold to 80° C. to mold a disk having a diameter of 3.5 cm and athickness of 2 mm. The obtained disk had a total light transmittance of90%, a Δb value of 0.30, high transparency and little coloration. Therewas observed neither a silver streak on its surface nor distortion.

EXAMPLE 5

[0244] A disk was molded using the resin obtained in Reference Example 3and the same injection molding machine as in Example 4. When molding wascarried out at a melting temperature of 320° C. and a mold temperatureof 80° C., a molded disk was obtained that had a total lighttransmittance of 90%, a Δ b value of 0.40, high transparency and littlecoloration. There was observed neither a silver streak on its surfacenor distortion as in Example 4.

EXAMPLE 6

[0245] A CD substrate having a diameter of 12 cm and a thickness of 1.2mm was molded using the resin obtained in Reference Example 2 and aninjection molding machine for optical disk substrates. A stamper forCD-ROM was used. When molding was carried out at a resin meltingtemperature of 300° C., a mold temperature of 90° C. and a cycle time of7 sec, a disk substrate with little coloration and high transparency wasobtained. The disk substrate had a total light transmittance of 90% anda Δb value of 0.54. A silver streak was not observed on its surface. Thedisk substrate had satisfactory mechanical properties with smalldistortions in both a circumferential direction and a radial directionof the disk substrate. When the disk surface on the stamper side wasobserved using an atomic force microscope (AFM) to check pittransferability, transferability was so satisfactory that pits were welltransferred according to the shape of the stamper. The surface waslittle roughened and the number of microvoids was small. When thein-plane birefringence of the disk substrate was measured in the radialdirection, the maximum value was 35 nm (measurement wavelength of 633nm, single pass). When the reduced viscosity of the molded disksubstrate was measured, η_(sp)/c was the same as that before molding,which was 0.40 dl/g. This means that there was no reduction in molecularweight by molding.

EXAMPLE 7

[0246] The resin melting temperature was elevated to 340° C. and themold temperature to 100° C. in an injection molding test in Example 6 tomold a CD, and a disk substrate with little coloration and hightransparency was obtained in the same manner as in Example 6. The disksubstrate had a total light transmittance of 89% and a Δb value of 0.65.A silver streak was not observed on its surface. The disk substrate hadsatisfactory mechanical properties with small distortions in both acircumferential direction and a radial direction of the disk substrate.When the disk substrate was observed under an AFM, pit transferabilitywas satisfactory, the surface was little roughened, and the number ofmicrovoids was small. When the in-plane birefringence of the disksubstrate was measured in a radial direction, the maximum value was 15nm (measurement wavelength of 633 nm, single pass). The disk substratehad a reduced viscosity η_(sp)/c of 0.40 dl/g, which was the same asthat before molding. This means that there was no reduction in molecularweight by molding.

EXAMPLE 8

[0247] The resin of Reference Example 2 and the injection moldingmachine used in Example 6 were used and the mold was replaced with amold for a digital video disk to mold a DVD substrate having a diameterof 12 cm and a thickness of 0.6 mm. A stamper for DVD-ROM was used. Whenmolding was carried out at a resin melting temperature of 370° C., amold temperature of 110° C. and a cycle time of 9.3 sec, a disksubstrate with little coloration and high transparency was obtained. Thedisk substrate had a total light transmittance of 89% and a Δb value of0.70. A silver streak was not observed on its surface. The disksubstrate had satisfactory mechanical properties with small distortionsin both a circumferential direction and a radial direction of the disksubstrate. When the disk surface on the stamper side was observed underan AFM, transferability was so satisfactory that pits were welltransferred according to the shape of the stamper. The surface waslittle roughened and the number of microvoids was small. When thein-plane birefringence of the disk substrate was measured in a radialdirection, the maximum value was 10 nm (measurement wavelength of 633nm, single pass). The molded disk substrate had a reduced viscosityη_(sp)/c of 0.40 dl/g, which was the same as that before molding. Thismeans that there was no reduction in molecular weight by molding.

COMPARATIVE EXAMPLE 2

[0248] An attempt was made to mold a CD substrate from the resinobtained in Reference Example 4 under the same conditions as in Example6. However, when the resin was injected into the mold and then taken outby opening the mold, the molded product was broken due to itsbrittleness. Thus, a disk substrate could not be molded.

COMPARATIVE EXAMPLE 3

[0249] A CD substrate was molded in the same manner as in Example 6except that the resin obtained in Reference Example 2 was used and thatthe resin melting temperature was set to 400° C. The obtained disksubstrate was burred. It had a total light transmittance of 87% and wasslightly colored with a Δb value of 1.36. A silver streak was slightlyobserved on its surface. The disk substrate had satisfactory mechanicalproperties with small distortions in both a circumferential directionand a radial direction of the disk substrate. When the disk substratewas measured by an AFM, pit transferability was satisfactory but highersurface roughness and more microvoids than those of Example 6 wereobserved. The molded disk substrate had a reduced viscosity η_(sp)/c of0.38 dl/g, which was a little lower than that before molding. This meansthat the decomposition of the resin took place during molding.

COMPARATIVE EXAMPLE 4

[0250] A CD substrate was molded in the same manner as in Example 7except that the resin obtained in Reference Example 2 was used and thatthe mold temperature was set to 140° C. The obtained substrate had atotal light transmittance of 90%, high transparency with a Δb value of0.46 and a maximum birefringence of 10 nm. Thus, the substrate wassatisfactory in terms of optical properties. However, since extremelylarge distortions in both a circumferential direction and a radialdirection of the substrate were observed on its surface, it could not beused as a disk substrate.

COMPARATIVE EXAMPLE 5

[0251] A disk was molded using the rein obtained in Reference Example 5under the same conditions as in Example 4. The obtained disk had a totallight transmittance of 75% and a Δb value of 3.86, very distinctcoloration and poor transparency. Therefore, it could not be used as anoptical material.

COMPARATIVE EXAMPLE 6

[0252] A disk was molded using the resin obtained in Reference Example 6under the same conditions as in Example 4. The obtained disk had a totallight transmittance of 82% and a Δb value of 2.06. Although the disk wasnot so distinctly colored, it had many silver streaks and burning andwas very hazy and poor in transparency.

COMPARATIVE EXAMPLE 7

[0253] For comparison, in the step of removing the final solvent inReference Example 2, the removal of a solvent was terminated whiletetrahydronaphthalene was still distilling off at a high temperature anda reduced pressure to obtain a hydrogenated α-olefin-dicyclopentadienecopolymer containing 1.8 wt % of tetrahydronaphthalene. When a disk wasmolded from the resin in the same manner as in Example 4, it had a lowtotal light transmittance of 83%, and many silver streaks and manymicrovoids were observed on its surface.

What is claimed is:
 1. A process for producing a hydrogenatedα-olefin-dicyclopentadiene copolymer comprising: (1) the step ofaddition-polymerization of an α-olefin having 2 or more carbon atoms anddicyclopentadiene in a hydrocarbon solvent in the presence of apolymerization catalyst, and then removing the polymerization catalystas required, to produce an α-olefin-dicyclopentadiene copolymer solutioncontaining unreacted dicyclopentadiene; (2) the step of adding ahydrogenation catalyst to the copolymer solution produced in the step(1) to hydrogenate the unsaturated double bonds of theα-olefin-dicyclopentadiene copolymer so as to produce a mixturecontaining a hydrogenated α-olefin-dicyclopentadiene copolymer; and (3)the step of distilling off tetrahydrodicyclopentadiene formed in thehydrogenation reaction of the step (2) from the mixture containing ahydrogenated α-olefin-dicyclopentadiene copolymer produced in theprevious step, wherein at least one of the following operations (i),(ii) and (iii) is carried out to ensure that a high-boiling hydrocarbonsolvent is existent in an amount of at least 10 parts by weight based on100 parts by weight of the hydrogenated α-olefin-dicyclopentadienecopolymer at the end of the step (3): (i) use of a high-boilinghydrocarbon solvent as at least part of the hydrocarbon solvent of thestep (1), (ii) addition of a high-boiling hydrocarbon solvent in thestep (2), and (iii) addition of a high-boiling hydrocarbon solvent inthe step (3); and the high-boiling hydrocarbon solvent contains at leasta hydrocarbon solvent having a boiling point at normal pressure of 195to 300° C. and an ignition point of 260° C. or more.
 2. The process ofclaim 1 , wherein the steps of removing the polymerization catalystand/or the hydrogenation catalyst from the mixture containing thehydrogenated α-olefin-dicyclopentadiene copolymer is further carried outafter the step (2) or the step (3).
 3. The process of claim 1 , whereinthe hydrocarbon solvent in the step (1) consists essentially of ahigh-boiling hydrocarbon solvent.
 4. The process of claim 1 , whichcarries out only the above operation (i).
 5. The process of claim 1 ,which carries out only the above operation (ii).
 6. The process of claim1 , wherein the high-boiling hydrocarbon solvent has a melting point of50° C. or less.
 7. The process of claim 1 , wherein the high-boilinghydrocarbon solvent is at least one member selected from the groupconsisting of 1-methylnaphthalene, 2-methylnaphthalene andtetrahydronaphthalene.
 8. The process of claim 1 , wherein thepolymerization catalyst is a metallocene-based catalyst.
 9. The processof claim 8 , wherein the metallocene-based catalyst comprises aco-catalyst and a compound of the group IV transition metal thatcontains a ligand having a cyclopentadienyl skeleton.
 10. The process ofclaim 9 , wherein the transition metal contained in themetallocene-based catalyst is zirconium and the co-catalyst is analuminoxane.
 11. The process of claim 9 , wherein the transition metalcontained in the metallocene-based catalyst is zirconium and theco-catalyst comprises an ionic boron compound and an alkylating agent.12. The process of claim 1 , wherein the polymerization catalyst is aZiegler-based catalyst.
 13. The process of claim 1 , wherein theα-olefin is ethylene.
 14. The process of claim 1 , wherein thehydrogenated α-olefin-dicyclopentadiene copolymer is obtained as ahigh-boiling hydrocarbon solvent solution.
 15. A process for producing ahydrogenated α-olefin-dicyclopentadiene copolymer comprising: (1′) thestep of addition-polymerization of an α-olefin having 2 or more carbonatoms and dicyclopentadiene in a hydrocarbon solvent in the presence ofa polymerization catalyst, and then removing the polymerization catalystas required, to produce an α-olefin-dicyclopentadiene copolymer solutioncontaining unreacted dicyclopentadiene; (2′) the step of distilling offthe unreacted dicyclopentadiene from the α-olefin-dicyclopentadienecopolymer solution containing the unreacted dicyclopentadiene producedin the step (1′) to produce an α-olefin-dicyclopentadiene copolymersolution containing substantially no dicyclopentadiene; and (3′) thestep of adding a hydrogenation catalyst to theα-olefin-dicyclopentadiene copolymer solution produced in the previousstep to hydrogenate the unsaturated double bonds of theα-olefin-dicyclopentadiene copolymer to produce a mixture containing ahydrogenated α-olefin-dicyclopentadiene copolymer, wherein at least oneof the following operations (i′) and (ii′) is carried out to ensure thata high-boiling hydrocarbon solvent is existent in an amount of at least10 parts by weight based on 100 parts by weight of theα-olefin-dicyclopentadiene copolymer at the end of the above step (2′):(i′) use of a high-boiling hydrocarbon solvent as at least part of thehydrocarbon solvent of step (1′), and (ii′) addition of a high-boilinghydrocarbon solvent in step (2′); and the high-boiling hydrocarbonsolvent contains at least a hydrocarbon solvent having a boiling pointat normal pressure of 195 to 300° C. and an ignition point of 260° C. ormore.
 16. The process of claim 15 , wherein the step of removing thepolymerization catalyst from the α-olefin-dicyclopentadiene copolymersolution is carried out after the step (2′).
 17. The process of claim 15, wherein the step of removing the polymerization catalyst and/or thehydrogenation catalyst from the mixture containing the hydrogenatedα-olefin-dicyclopentadiene copolymer is further carried out after thestep (3′).
 18. The process of claim 15 , wherein the hydrocarbon solventin the step (1′) consists essentially of a high-boiling hydrocarbonsolvent.
 19. The process of claim 15 , which carries out only the aboveoperation (i′).
 20. The process of claim 15 , wherein the high-boilinghydrocarbon solvent has a melting point of 50° C. or less.
 21. Theprocess of claim 15 , wherein the high-boiling hydrocarbon solvent is atleast one member selected from the group consisting of1-methylnaphthalene, 2-methylnaphthalene and tetrahydronaphthalene. 22.The process of claim 15 , wherein the polymerization catalyst is ametallocene-based catalyst.
 23. The process of claim 22 , wherein themetallocene-based catalyst comprises a co-catalyst and a compound of thegroup IV transition metal that contains a ligand having acyclopentadienyl skeleton.
 24. The process of claim 23 , wherein thetransition metal contained in the metallocene-based catalyst iszirconium and the co-catalyst is an aluminoxane.
 25. The process ofclaim 23 , wherein the transition metal contained in themetallocene-based catalyst is zirconium and the co-catalyst comprises anionic boron compound and an alkylating agent.
 26. The process of claim15 , wherein the polymerization catalyst is a Ziegler-based catalyst.27. The process of claim 15 , wherein the α-olefin is ethylene.
 28. Theprocess of claim 15 , wherein the hydrogenatedα-olefin-dicyclopentadiene copolymer is obtained as a high-boilinghydrocarbon solvent solution.
 29. A method for melt-molding ahydrogenated α-olefin-dicyclopentadiene copolymer, which comprises thesteps of introducing a hydrogenated α-olefin-dicyclopentadiene copolymerwhich has a reduced viscosity η_(sp)/c, measured at 30° C. in a toluenesolution having a concentration of 0.5 g/dl, of 0.25 to 3 dl/g and whichis selected from the group consisting of: (i) a copolymer comprisingrecurring units represented by the following formula (A):

wherein R¹ is a hydrogen atom or a saturated aliphatic hydrocarbon grouphaving 1 to 16 carbon atoms, and recurring units represented by thefollowing formula (B):

wherein R² is a hydrogen atom or a saturated aliphatic hydrocarbon grouphaving 1 to 16 carbon atoms, the molar ratio of the recurring unit (A)to the recurring unit (B) being 0 to 39/100 to 61, and (ii) a copolymercomprising recurring units represented by the above formula (A),recurring units represented by the above formula (B), recurring unitsrepresented by the following formula (C):

wherein n is 0 or 1, m is 0 or a positive integer, p is 0 or 1, R³to R²²are the same or different and are each a hydrogen atom, halogen atom,aromatic hydrocarbon group having 6 to 10 carbon atoms, or saturated orunsaturated aliphatic hydrocarbon group having 1 to 12 carbon atoms,either R¹⁹ and R²⁰ or R²¹ and R²² may form an alkylidene group, and oneof R¹⁹ and R²⁰ and one of R²¹ or R²² may form a ring which may have adouble bond or aromatic ring, and recurring units represented by thefollowing formula (D):

wherein q is an integer of 2 to 8, the ratio of the total number of molsof the recurring units (A) and (B) to the total number of mols of therecurring units (C) and (D) being 95 to 99.9/5 to 0.1, the molar ratioof the recurring unit (A) to the recurring unit (B) being 0 to 39/100 to61, and the molar ratio of the recurring unit (D) to the recurring unit(C) being 0 to 95/100 to 5, into a mold maintained at a temperaturerange from a temperature 100° C. lower than the glass transitiontemperature of the copolymer to a temperature 10° C. lower than theglass transition temperature of the copolymer and molding it at a moltenpolymer temperature of 230 to 380° C.
 30. The molding method of claim 29, wherein the content of the gel contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer is 1 wt % or less.
 31. The moldingmethod of claim 29 , wherein the content of the residual catalyst metalcontained in the hydrogenated α-olefin-dicyclopentadiene copolymer is 10ppm or less.
 32. The molding method of claim 29 , wherein the content ofthe hydrocarbon volatile components contained in the hydrogenatedα-olefin-dicyclopentadiene copolymer is 0.1 wt % at most.
 33. Themolding method of claim 29 , wherein a phenol compound and/or aphosphorus compound is used as an antioxidant in an amount of 0.01 to 3wt % based on the hydrogenated α-olefin-dicyclopentadiene copolymer. 34.An optical disk substrate obtained by the molding method of claim 29 .35. An optical lens obtained by the molding method of claim 29 .
 36. Anoptical sheet obtained by the molding method of claim 29 .